Ultrasound Obstet Gynecol 2014; 44: 82–89 Published online 28 May 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/uog.13324
Sonographic pattern of fetal head descent: relationship with duration of active second stage of labor and occiput position at delivery T. GHI*, E. MARONI*, A. YOUSSEF*, A. M. MORSELLI-LABATE†, A. PACCAPELO†, E. MONTAGUTI*, N. RIZZO* and G. PILU* *Department of Obstetrics and Gynecology, Sant’Orsola-Malpighi Hospital, Alma Mater-University of Bologna, Bologna, Italy; †Department of Medical and Surgical Sciences, Alma Mater-University of Bologna, Bologna, Italy
K E Y W O R D S: intrapartum ultrasound; labor; persistent occiput posterior; second stage; three-dimensional
ABSTRACT Objectives The objectives of this study were firstly to assess the longitudinal changes of various sonographic parameters of fetal head progression in relation to length of active second stage of labor, and secondly to compare ultrasound findings obtained longitudinally among fetuses with persistent occiput posterior (OP) vs those with persistent occiput anterior (OA) position. Methods From a series of nulliparous low-risk women at term attending the labor ward of our university hospital, transperineal ultrasound volumes were prospectively acquired at the beginning of the active second stage (T1) and at 40-min intervals thereafter until delivery (T2, T3). Sonographic parameters were derived from offline analysis of each volume, including the angle of progression (AoP), progression distance (PD), head–symphysis distance (HSD), head direction (HD) and midline angle. These parameters were compared between patients who delivered within 60 min from the beginning of the active second stage of labor (early delivery) and those who remained undelivered by that time (late delivery). Fetal head position was determined from stored digital images of transabdominal examinations performed at the beginning of the active second stage. Comparison was performed between fetuses with OA and those with persistent OP position at delivery. Results Spontaneous vaginal delivery was achieved in 58 (81.7%) cases, whereas vacuum extraction and Cesarean section were performed in eight (11.3%) and five (7.0%) cases, respectively. Delivery was achieved within 60 min from the beginning of the active second stage in 44 (62.0%) patients. In the early vs late delivery groups, measurements of AoP, HSD and PD at T1 were significantly
different (AoP, 143.9 ± 20.5◦ vs 125.3 ± 15.0◦ , P < 0.001; HSD, 14.8 ± 4.5 mm vs 20.9 ± 5.8 mm, P < 0.001; PD, 44.0 ± 14.1 vs 35.0 ± 13.1 mm, P = 0.008). On logistic regression analysis of data obtained at T1, maternal body mass index, oxytocin administration, neonatal birth weight and HSD appeared to predict independently duration of the active second stage. Among fetuses delivering in the OP position (n = 10, 13.5%), Cesarean delivery was significantly more common than in those delivering in the OA position (n = 5 (50.0%) vs n = 2 (3.1%), P = 0.001). Women with persistent OP position compared with OA showed a significantly different AoP at T1 (122 ± 17◦ vs 138 ± 20◦ , P = 0.016), HD and HSD at T1 (HD, 112 ± 17 mm vs 86 ± 19 mm, P < 0.001; HSD, 16.5 ± 5.4 mm vs 22.8 ± 6.6 mm, P = 0.008) and at T2 (HD, 120 ± 16 vs 82 ± 27 mm, P = 0.008; HSD, 12.6 ± 3.4 mm vs 18.5 ± 5.4 mm, P = 0.038). Conclusions AoP, PD and HSD are significantly different between patients undergoing delivery before or after 60 min from the beginning of the active second stage of labor. Ultrasound parameters are among the significant predictors of duration of the active second stage. Moreover, in fetuses persisting in the OP position vs those delivering in the OA position, fetal head progression seems to differ at early phases of the active second stage. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
INTRODUCTION Prediction of vaginal delivery in a laboring woman is traditionally based upon assessment of progression of cervical dilatation and fetal head descent. When progression is poor, arrest of labor – currently the leading
Correspondence to: Dr T. Ghi, Obstetrics and Prenatal Medicine Unit, Sant’Orsola-Malpighi University Hospital, University of Bologna, Italy, Via Massarenti 13, 40138 Bologna, Italy (e-mail: [email protected]) Accepted: 22 January 2014
Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
ORIGINAL PAPER
Fetal head descent, second stage of labor and occiput position at delivery indication for primary Cesarean section in the USA – is diagnosed and obstetric intervention is needed1 . Extreme variability exists in the clinical definition of dystocia. In the active second stage, different criteria are used according to parity or epidural administration1 . A bulletin issued by a panel of experts states ‘If progress is made, the duration alone does not mandate delivery’1 . However some large studies have consistently shown that the longer the active second stage, the lower the chance of spontaneous vaginal delivery and the higher the risk of serious maternal or perinatal events2,3 . Fetuses with a persistent occiput posterior (OP) position in the second stage are at higher risk of dystocia or labor complications. In this group a higher risk of Cesarean section or need for operative vaginal delivery is consistently reported, and a globally increased incidence of maternal and perinatal complications is widely acknowledged4 – 7 . Ultrasonography has recently been used to assess fetal head progression during the second stage of labor8 – 16 , and sonographic data have been compared with digital findings12 – 15 . However, studies on sonographic evaluation of head descent have mostly focused on fetuses with occiput anterior (OA) position, while those with persistent OP position have been excluded or not assessed separately10 . The aims of this study were firstly to assess the longitudinal changes of various sonographic parameters of fetal head progression in relation to length of the active second stage of labor and secondly to compare ultrasound findings obtained longitudinally among fetuses with persistent OP vs those with persistent OA position.
SUBJECTS AND METHODS Transperineal ultrasound volumes were prospectively acquired from a non-consecutive series of nulliparous women attending the labor ward of our university hospital with uncomplicated singleton pregnancies at term (≥ 37 weeks) and with fetuses in cephalic presentation. Data from 71 women recruited between November 2010 and November 2011 were used for the longitudinal analysis of sonographic parameters. Data from these 71 women have been published previously16 . For comparison of occiput position, data from another three OP cases recruited up to September 2012 were included. Women were considered eligible regardless of whether labor was spontaneous or induced. Recruitment was carried out at the onset of labor when a trained investigator, with at least 3 years of experience in obstetric ultrasound, was available in the labor ward for the purposes of the study. Women were considered to be in the active second stage when they reached full cervical dilatation and began active pushing. Digital examination was performed before ultrasound scan to determine fetal head station and position. Ultrasonography was performed using a portable machine (Voluson i, GE Medical Systems, Zipf, Austria) equipped with a volumetric probe by one of the investigators (T.G.,
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E.M., A.Y., E.M. or G.P.), who was blinded to the findings on clinical examination. Ultrasound volume acquisition was carried out with an infrapubic or translabial approach in the absence of maternal pushing and uterine contractions, as described elsewhere12 . The woman’s bladder was kept empty by means of intermittent catheterization throughout the whole active second stage of labor, including during ultrasound examination. Both digital examination and ultrasound scan were performed at the beginning of the active second stage (T1) and at 40-min intervals thereafter (T2, T3) until delivery. All volumes were transferred to a personal computer equipped with dedicated software (4D view 9.0 and Sono-VCAD labor; GE Medical Systems) for offline analysis following delivery. Fetal head position at the beginning of the active second stage had not been prospectively assessed in these 71 women, and was retrospectively derived from digital images obtained by transabdominal and transperineal ultrasound and stored in the archive of the machine. In the extended study period, the fetal occiput position was prospectively checked by transabdominal ultrasound. The occiput position was labeled as anterior, posterior or transverse (right or left). The occiput position was defined as transverse when the midline angle was about 90◦ 11 . Fetal occiput position was visually determined at delivery (either vaginal or abdominal). Sonographic parameters obtained at 40-min intervals were compared between OA and OP fetuses. Volume analysis was performed after delivery and did not influence clinical management of labor by the attending physician, who was blinded to the sonographic findings. Patients were excluded from the study if they underwent Cesarean section or instrumental vaginal delivery in the second stage solely because of suspected fetal distress. For offline analysis, the volume was opened in the multiplanar mode in which the sagittal plane was displayed on Panel A and the axial and coronal planes on Panels B and C, respectively. Each volume was processed using the static-VCI algorithm in order to improve image resolution in the reconstructed planes12 . Volume alignment was obtained using the pubis and the urethra as reference points as previously described12 . Subsequently, the Sono-VCAD labor software was launched and, using the midsagittal plane, the following data were calculated: angle of progression (AoP; defined as the angle between the longitudinal axis of the pubic bone and a line joining the lowest edge of the pubis to the lowest convexity of the fetal skull)9 ; progression distance (PD; defined as the distance (mm) between the infrapubic line and the lowest part of the fetal skull)17 ; head–symphysis distance (HSD; defined as the distance between the lowest edge of the symphysis pubis and the nearest point of the fetal skull along the infrapubic line)16 ; and head direction (evaluated only for the occiput position analysis and defined as the angle between the infrapubic line and the major longitudinal axis of the fetal head)8 . The latter line is automatically generated by the software as the one
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perpendicular to the biparietal diameter. Switching from the sagittal to the axial plane, the midline angle (MLA; defined as the angle between the anteroposterior axis of the maternal pelvis and the head midline) was calculated11 . The study protocol was approved by the local ethics committee (No: 137/2010/O/Oss) and an informed consent form was signed at the onset of labor by each eligible patient. The study protocol conforms to the ethical guidelines of the ‘World Medical Association (WMA) Declaration of Helsinki – Ethical Principles for Medical Research Involving Human Subjects’ adopted by the 18th WMA General Assembly, Helsinki, Finland, June 1964 and amended by the 59th WMA General Assembly, Seoul, South Korea, October 2008.
Statistical analysis Data are reported as mean ± SD, median and range or frequencies. Data were compared between patients who delivered within 60 min from the beginning of the active second stage of labor (early delivery) and those who remained undelivered by that time (late delivery) by means of the Fisher’s exact, Kruskal–Wallis and Pearson chi-square tests. Comparisons between the two groups were made without taking into account the fetal occiput position at the beginning of the active second stage or at delivery. Receiver–operating characteristics (ROC) curves were constructed in order to estimate the accuracy of ultrasound parameters in predicting duration of the active second stage. The area under the ROC curve (AUC) was computed together with the 95% CI. The estimated ranges of best cut-off values were calculated by means of a maximum likelihood ratio method18 . Stepwise backward multivariable logistic regression analysis was applied in order to identify which variables independently predicted duration of the active second stage. In order to estimate duration of the active second stage according to ultrasound parameters, we used the Kaplan–Meier procedure, and the log-rank test for
trend was applied. In these analyses the ultrasound parameters were categorized according to quartile values (computed by using the data of the first ultrasound examination at the beginning of active maternal pushing and by applying the empirical-distribution-with-averaging method), and operative deliveries were considered as censored data. The SPSS version 13.0 for Windows statistical package (SPPS, Inc., Chicago, IL, USA) was used to analyze data and two-tailed P < 0.05 was considered statistically significant.
RESULTS Of the 71 initially recruited patients, 58 (81.7%) underwent spontaneous vaginal delivery, while vacuum extraction and Cesarean section was performed owing to dystocia in eight (11.3%) and five (7.0%) cases, respectively. The mean duration of the active second stage was 56.0 ± 40.2 min (median, 44 (range, 7–191)) min. Overall, 44 patients (62.0%) were delivered within 60 min from the beginning of the active second stage (early delivery group; mean duration of active second stage, 31.0 ± 13.4 min) while 27 (38.0%) remained undelivered by that time (late delivery group; mean duration of active second stage, 96.8 ± 35.7 min). A comparison of demographic and labor characteristics of these two groups is given in Table 1. The only statistically significant difference between the two groups was a greater birth weight in the late vs early delivery group (3654 ± 360 vs 3313 ± 398 g, P < 0.001). Other characteristics were similar between the groups, including occiput position at delivery and rate of epidural administration. The rate of operative delivery, including Cesarean section and vacuum extraction, was slightly higher in the late delivery group, although this difference was not statistically significant. Sonographic data obtained in the two groups are shown in Table 2. In the late vs early delivery group, the AoP
Table 1 Clinical details of study population of 71 women at beginning of active second stage of labor, according to its duration: < 60 min (early delivery) or > 60 min (late delivery) Parameter Maternal age (years) Body mass index (kg/m2 ) Gestational age at delivery (weeks) Birth weight (g) Oxytocin administration Epidural analgesia Spontaneous delivery Operative delivery Vacuum extraction Cesarean section Duration of labor (min)‡ Occiput position at delivery Anterior Posterior
Early delivery (n = 44)
Late delivery (n = 27)
P
31.0 ± 4.8; 32 (20–41) 27.8 ± 4.1; 27.3 (18.4–37.2) 39.5 ± 1.2; 39.6 (37.3–41.7) 3313 ± 398; 3242 (2450–4150) 25 (56.8) 24 (54.5) 39 (88.6) 5 (11.4) 4 (9.1) 1 (2.3) 233.5 ± 118.6; 225 (30–501)
31.4 ± 5.1; 32 (21–41) 26.7 ± 3.4; 25.9 (17.9–33.8) 39.4 ± 1.2; 39.4 (37.3–41.7) 3654 ± 360; 3625 (2740–4520) 21 (77.8) 17 (63.0) 19 (70.4) 8 (29.6) 4 (14.8) 4 (14.8) 375.7 ± 138.6; 367 (190–824)
0.647* 0.349* 0.652* < 0.001* 0.081† 0.622† 0.065†
40 (90.9) 4 (9.1)
24 (88.9) 3 (11.1)
< 0.001* 1.000†
Data are expressed as mean ± SD; median (range) or as n (%). *Kruskal–Wallis test. †Fisher’s exact test. ‡Duration of labor: time elapsed from beginning of labor (3–4-cm dilatation, effaced cervix, regular uterine contractions) to delivery.
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Table 2 Sonographic data at beginning of active second stage of labor (T1) and at 40-min intervals thereafter (T2, T3) in 71 women, according to duration of active second stage: < 60 min (early delivery) or > 60 min (late delivery) Variable/time point
Early delivery (n = 44)
Late delivery (n = 27)
P*
143.9 ± 20.5; 142.5 (102–213) 161.0 ± 8.5; 161 (155–167) —
125.3 ± 15.0; 124 (102–165) 144.4 ± 17.7; 142 (115–180) 145.6 ± 30.8; 135 (121–209)
< 0.001 0.179 —
44.0 ± 14.1; 45 (12–68) 55.5 ± 5.0; 55.5 (51–59) —
35.0 ± 13.1; 37 (11–64) 47.1 ± 12.7; 46 (18–69) 46.3 ± 18.3; 40 (30–83)
0.008 0.211 —
14.8 ± 4.5; 14 (6–33) 12.5 ± 3.5; 12.5 (10–15) —
20.9 ± 5.8; 21 (10–34) 13.4 ± 4.3; 12 (7–18) 12.3 ± 4.2; 12 (7–18)
< 0.001 0.889 —
34.4 ± 16.4; 29 (7–69) 12.5 ± 2.1; 12.5 (11–14) —
41.1 ± 28.9; 36 (0–127) 28.2 ± 20.0; 28 (1–101) 25.3 ± 10.0; 26 (13–38)
0.445 0.138 —
◦
Angle of progression ( ) T1 (n = 44 vs n = 27) T2 (n = 2 vs n = 25) T3 (n = 0 vs n = 7) Progression distance (mm) T1 (n = 44 vs n = 27) T2 (n = 2 vs n = 25) T3 (n = 0 vs n = 7) Head–symphysis distance (mm) T1 (n = 44 vs n = 27) T2 (n = 2 vs n = 25) T3 (n = 0 vs n = 7) Midline angle (◦ ) T1 (n = 44 vs n = 27) T2 (n = 2 vs n = 25) T3 (n = 0 vs n = 7)
Data are expressed as mean ± SD and median (range). *Kruskal–Wallis test.
1.0 0.9 0.8
Sensitivity
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 – Specificity
Figure 1 Receiver–operating characteristics curves for angle of ), progression distance ( ) and progression ( ) at onset of active second stage of head–symphysis distance ( labor in a cohort of 71 women, showing accuracy of these ultrasonographic parameters in discriminating late (> 60 min) from early (< 60 min) delivery.
and PD were significantly smaller at T1 whereas the HSD was significantly greater in the former group at the same time frame. No significant difference in the MLA was found at any time. At T2, no difference was found in any sonographic parameter; however, of those patients assessed at this time point only two delivered within an hour of the start of the active second stage, severely limiting the power of statistical tests. In order to evaluate the accuracy of ultrasound parameters in the prediction of late delivery, ROC curves of the parameters that were found to be statistically significantly different between the two groups were constructed (Figure 1). The AUCs are reported in Table 3 together with sensitivities, specificities and predictive values obtained by subdividing the study population according to the best cut-off values. Kaplan–Meier analysis was applied in order to estimate duration of the spontaneous active second stage in the whole population according to the distribution of the sonographic parameters. Greater values of AoP and PD at the beginning of the active second stage correlated with a shorter time to delivery, while a direct relationship was found between HSD and duration of active second stage (Figure 2 and Table 4). The relationship between clinical and sonographic parameters and late delivery was analyzed by means
Table 3 Summary statistics of receiver–operating characteristics (ROC) curve analysis for angle of progression (AoP), progression distance (PD) and head–symphysis distance (HSD) evaluated in 71 patients at beginning of active second stage of labor in predicting late delivery (> 60 min)
Variable AoP PD HSD
Area under ROC curve (95% CI)
Estimated best cut-off range
Sensitivity (n/N (%))
Specificity (n/N (%))
PPV (n/N (%))
NPV (n/N (%))
0.777 (0.666–0.888) 0.688 (0.563–0.814) 0.816 (0.709–0.781)
139–142◦ 38–39 mm 19–20 mm
25/27 (92.6) 20/27 (74.1) 16/27 (59.3)
24/44 (54.5) 29/44 (65.9) 42/44 (95.5)
25/45 (55.6) 20/35 (57.1) 16/18 (88.9)
24/26 (92.3) 29/36 (80.6) 42/53 (79.2)
NPV, negative predictive value; PPV, positive predictive value.
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Proportion of pregnancies undelivered
(a)
Table 4 Mean duration of active second stage of labor estimated by Kaplan–Meier analysis performed for angle of progression, progression distance and head–symphysis distance in 71 patients at beginning of active stage, stratified by quartiles of each variable
1.0
0.8
Parameter 0.6
0.4
0.2
0.0 0
50
100
150
200
Duration of second stage of labor (min)
Proportion of pregnancies undelivered
(b)
1.0
95% CI (min)*
96.3 ± 13.7 62.6 ± 10.7 50.2 ± 7.5 37.6 ± 5.1
69.4–123.2 41.7–83.5 35.4–64.9 27.6–47.6
88.5 ± 16.6 73.6 ± 10.3 52.4 ± 7.8 38.4 ± 4.5
56.0–121.0 53.4–93.7 37.1–67.6 29.5–47.3
39.8 ± 4.6 37.7 ± 4.6 63.2 ± 10.8 124.8 ± 13.2
30.9–48.8 28.7–46.7 42.0–84.5 99.0–150.6
P† < 0.001
0.001
< 0.001
*95% CI of estimated mean length of active second stage of labor. †Log-rank test for trend. 0.8
0.6
0.4
0.2
0.0 0
50
100
150
200
Duration of second stage of labor (min) (c) 1.0 Proportion of pregnancies undelivered
Angle of progression 1st quartile (≤ 122◦ ) 2nd quartile (123–134◦ ) 3rd quartile (135–150◦ ) 4th quartile (> 150◦ ) Progression distance 1st quartile (≤ 30 mm) 2nd quartile (31–39 mm) 3rd quartile (40–52 mm) 4th quartile (> 52 mm) Head–symphysis distance 1st quartile (≤ 12 mm) 2nd quartile (13–17 mm) 3rd quartile (18–20 mm) 4th quartile (> 20 mm)
Mean ± SE (min)
0.8
0.6
0.4
0.2
0.0 0
50
100
150
200
Duration of second stage of labor (min)
Figure 2 Kaplan–Meier analysis showing time to delivery in relation to angle of progression (a), progression distance (b) and head–symphysis distance (c) at beginning of active second stage of labor. Data are stratified according to the quartiles of each variable: , 1st quartile; , 2nd quartile; , 3rd quartile; , 4th quartile.
Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
of univariable and multivariable logistic regression (Table S1). Duration of the active second stage was significantly related to all sonographic parameters, apart from MLA, at the beginning of the active second stage. Multivariable analysis showed that, at the beginning of the active second stage, HSD together with maternal body mass index, oxytocin administration and neonatal birth weight appeared to predict independently duration of the active second stage. Demographic details and labor outcome according to fetal occiput position at delivery are summarized in Table S2. Patient characteristics were similar between the two groups, including the rate of scheduled epidural administration. Of the 10 fetuses delivered in a persistent OP position, the rate of Cesarean section was much higher than in those delivered in the OA position (n = 5 (50.0%) vs n = 2 (3.1%), P < 0.001), while rates of vacuum extraction were comparable (n = 1 (10%) vs n = 8 (12.5%), P = 0.650). Sonographic data obtained in the two groups are reported in Table S3. Women with a persistent OP position showed a significantly smaller AoP at T1 than did those with an OA position (122 ± 17◦ vs 138 ± 20◦ , P = 0.016). Furthermore, HD and HSD were significantly different in the two groups at T1 (HD, 112 ± 17 mm vs 86 ± 19 mm, P < 0.001; HSD, 16.5 ± 5.4 mm vs 22.8 ± 6.6 mm, P = 0.008) and T2 (HD, 120 ± 16 mm vs 82 ± 27 mm, P = 0.008; HSD, 12.6 ± 3.4 mm vs 18.5 ± 5.4 mm, P = 0.038). No significant differences were observed for PD and MLA. Only one case in the OP position remained undelivered at T3, which did not allow comparison of sonographic data with fetuses in the OA position at this time point. However, in this case the fetal head showed an upward direction, and both AoP and HSD were similar to values obtained from cases of OA.
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OA position
(a)
(b)
(c)
(b)
(c)
OP position
(a)
Figure 3 Schematic representation of fetal head progression through maternal pelvis in occiput anterior (OA) and occiput posterior (OP) fetuses. In vertex-presenting fetuses, head descent converts from downward at inlet (a) to horizontal at midpelvis (b) to upward at outlet (c). OP fetuses maintain a downward direction with respect to the pubic bone from inlet to midpelvis (a,b) and only after passing the ischial spines do they abruptly twist up towards the outlet (c) only in those cases that are delivered vaginally.
DISCUSSION
Figure 4 Sonographic demonstration of head descent in the birth canal in occiput anterior (OA) and occiput posterior (OP) fetuses. At the beginning of active second stage (T1), in OP fetuses the head was directed more downward and the head–symphysis distance (HSD) appeared greater than that of OA fetuses. After 40 min (T2), among the OP group the fetal head maintained a downward direction and a significantly greater HSD was still noted.
Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
Our study provides original data on the longitudinal changes of several ultrasound parameters during the active second stage of labor; we found a significant correlation between ultrasound findings and duration of the active second stage. Multivariable logistic regression analysis demonstrated that sonographic findings were significant predictors of the active second stage length together with birth weight, maternal body mass index and oxytocin augmentation. This is in agreement with previous studies by Barbera et al.9 , who first reported that the narrower the angle of progression at the beginning of the active second stage, the longer is the time to delivery. Our data suggest that a similar correlation also exists with other sonographic measurements, including HSD and PD. We suggest that this is a valuable observation, because at present it is uncertain which is the most convenient ultrasound parameter for evaluating descent of the fetal head19,20 . Many advocate the use of a simple approach to aid operators with limited experience of diagnostic ultrasound21 . For this reason, we have previously proposed the use of HSD, a highly reproducible linear measurement15 . HSD demonstrates a strong correlation with the duration of the active second stage, and is no more difficult to obtain than is AoP. As shown in Table 4, if HSD is greater than 20 mm at the beginning of the active second stage, the length of this stage is likely to exceed 60 min, with a mean duration of 1.5 h. It is well established that a prolonged second stage is associated with a lower chance of spontaneous vaginal
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delivery and an increased risk of maternal and fetal complications2,3,22 . Prediction of the time to delivery would be useful in many different clinical situations, particularly those involving abnormal fetal electronic monitoring and patients with a reduced tolerance to physical exertion because of cardiac disease or other disorders. Our study also showed that there is a measurable difference in sonographic findings of head descent when the occiput is posterior rather than anterior. Fetuses with OA follow the curved path of the birth canal (Figure 3) and this results in a progressive increase in the AoP and PD, with a simultaneous decrease in HSD. On the other hand, with OP the head descends maintaining a downward direction for a much longer time, until the forehead has passed the pubic bone. This results initially in a smaller AoP and a greater HSD than in fetuses with OA presentation. While the head descends the AoP increases slowly while the HSD remains constant or increases. Among the OP fetuses of our series smaller values of both AoP and HD and a greater HSD were indeed documented by ultrasound up to 40 min from the beginning of the active second stage (Figure 4). A more horizontal or downward fetal HD with respect to the pubic bone has been sonographically witnessed by others among fetuses with a persistent OP position in the active second stage8,14 . This confirms that the mechanism of vaginal delivery of OP fetuses requires an increased distension of the perineum to accommodate a greater degree of downward descent of the fetal head, until the forehead has completely passed the pubic bone23 . At this time, flexion of the head becomes possible and sonography demonstrates a marked decrease in HSD. Owing to this upward change of fetal head progression, the descent path of OP fetuses is likely to become similar to that of OA fetuses in the later phases of the second stage. However of the fetuses delivered vaginally in persistent OP position, only one case of this series remained undelivered after 80 min, preventing further comparison of sonographic measurements with fetuses delivered in the OA position. Interestingly the PD does not seem to vary significantly between OP and OA cases, and this suggests that it is not the depth but rather the direction of the fetal head descent that is affected in the former group, leading to an increased chance of dystocia and need for Cesarean section and possibly to the increased rate of failure in instrumental vaginal delivery. On the other hand, the MLA is comparable in OP and OA fetuses. This seems to indicate that OP fetuses engage along the oblique diameter of the pelvic inlet and undergo a movement of internal rotation at the midpelvis similarly to OA fetuses. We acknowledge several limitations of our study. The most important one is the limited number of cases. We aimed to obtain longitudinal evaluations, but the longer the interval from the beginning of the active second stage, the smaller the number of patients who remained undelivered and were available for comparison. We believe that this is the most likely explanation for the absence of significant differences in sonographic findings in the advanced active second stage. The lack of a significant
Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
difference in the MLA in patients who delivered early vs those who delivered late is almost certainly due to the fact that head rotation only occurs at an advanced stage of fetal head descent. The lack of a significant difference in the rate of operative delivery between patients who delivered early vs those who delivered late is also probably a consequence of the small numbers in the study. In conclusion, our study has shown that sonographic findings predict the duration of the active second stage of labor. We have also described the sonographic appearance of the pattern of head descent of fetuses with OP presentation, and this may prove useful in the future to set a standard to diagnose abnormal labor, which is very frequent in these cases. At the moment the use of ultrasound in labor is limited to the research setting. Our study may represent a step towards the introduction of this tool in clinical practice.
REFERENCES 1. American College of Obstetrics and Gynecology Committee on Practice Bulletins-Obstetrics. ACOG Practice Bulletin Number 49, December 2003: Dystocia and augmentation of labor. Obstet Gynecol 2003; 102: 1445–1454. 2. Cheng YW, Hopkins LM, Caughey AB. How long is too long: Does a prolonged second stage of labor in nulliparous women affect maternal and neonatal outcomes? Am J Obstet Gynecol 2004; 191: 933–938. 3. Le Ray C, Audibert F, Goffinet F, Fraser W. When to stop pushing: effects of duration of second-stage expulsion efforts on maternal and neonatal outcomes in nulliparous women with epidural analgesia. Am J Obstet Gynecol 2009; 201: 361.e1–7. 4. Sen´ecal J, Xiong X, Fraser WD; Pushing Early Or Pushing Late with Epidural study group. Effect of fetal position on secondstage duration and labor outcome. Obstet Gynecol 2005; 105: 763–772. 5. Lieberman E, Davidson K, Lee-Parritz A, Shearer E. Changes in fetal position during labor and their association with epidural analgesia. Obstet Gynecol 2005; 105: 974–982. 6. Fitzpatrick M, McQuillan K, O’Herlihy C. Influence of persistent occiput posterior position on delivery outcome. Obstet Gynecol 2001; 98: 1027–1031. 7. Ponkey SE, Cohen AP, Heffner LJ, Lieberman E. Persistent fetal occiput posterior position: obstetric outcomes. Obstet Gynecol 2003; 101: 915–920. ¨ 8. Henrich W, Dudenhausen J, Fuchs I, Kamena A, Tutschek B. Intrapartum translabial ultrasound (ITU): sonographic landmarks and correlation with successful vacuum extraction. Ultrasound Obstet Gynecol 2006; 28: 753–760. 9. Barbera AF, Pombar X, Perugino G, Lezotte DC, Hobbins JC. A new method to assess fetal head descent in labor with transperineal ultrasound. Ultrasound Obstet Gynecol 2009; 33: 313–319. ¨ 10. Kalache KD, Duckelmann AM, Michaelis SA, Lange J, Cichon G, Dudenhausen JW. Transperineal ultrasound imaging in prolonged second stage of labor with occipitoanterior presenting fetuses: how well does the ‘angle of progression’ predict the mode of delivery? Ultrasound Obstet Gynecol 2009; 33: 326–330. 11. Ghi T, Farina A, Pedrazzi A, Rizzo N, Pelusi G, Pilu G. Diagnosis of station and rotation of the fetal head in the second stage of labor with intrapartum translabial ultrasound. Ultrasound Obstet Gynecol 2009; 33: 331–336. 12. Ghi T, Contro E, Farina A, Nobile M, Pilu G. Three-dimensional ultrasound in monitoring progression of labor: a reproducibility study. Ultrasound Obstet Gynecol 2010; 36: 500–506.
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Fetal head descent, second stage of labor and occiput position at delivery 13. Molina FS, Terra R, Carrillo MP, Puertas A, Nicolaides KH. What is the most reliable ultrasound parameter for assessment of fetal head descent? Ultrasound Obstet Gynecol 2010; 36: 493–499. 14. Tutschek B, Braun T, Chantraine F, Henrich W. A study of progress of labour using intrapartum translabial ultrasound, assessing head station, direction, and angle of descent. BJOG 2011; 118: 62–69. 15. Youssef A, Maroni E, Ragusa A, De Musso F, Salsi G, Iammarino MT, Paccapelo A, Rizzo N, Pilu G, Ghi T. The fetal head–symphysis distance: a simple and reliable ultrasound index of fetal station in labor. Ultrasound Obstet Gynecol 2013; 41: 419–424. 16. Ghi T, Youssef A, Maroni E, Arcangeli T, De Musso F, Bellussi F, Nanni M, Giorgetta F, Morselli-Labate AM, Iammarino MT, Paccapelo A, Cariello L, Rizzo N, Pilu G. Intrapartum transperineal ultrasound assessment of fetal head progression in active second stage of labor and mode of delivery. Ultrasound Obstet Gynecol 2013; 41: 430–435. 17. Dietz HP, Lanzarone V. Measuring engagement of the fetal head: validity and reproducibility of a new ultrasound technique. Ultrasound Obstet Gynecol 2005; 25: 165–168.
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18. Pezzilli R, Billi P, Miniero R, Fiocchi M, Cappelletti O, Morselli-Labate AM, Barakat B, Sprovieri G, Miglioli M. Serum interleukin-6, interleukin-8, and beta 2-microglobulin in early assessment of severity of acute pancreatitis. Comparison with serum C-reactive protein. Dig Dis Sci 1995; 40: 2341–2348. 19. Tutschek B, Torkildsen EA, Eggebø TM. Comparison between ultrasound parameters and clinical examination to assess fetal head station in labor. Ultrasound Obstet Gynecol 2013; 41: 425–429. ˚ Eggebø TM. Prediction of delivery 20. Torkildsen EA, Salvesen KA, mode with transperineal ultrasound in women with prolonged first stage of labor. Ultrasound Obstet Gynecol 2011; 37: 702–708. 21. Youssef A, Bellussi F, Maroni E, Pilu G, Rizzo N, Ghi T. Ultrasound in labor: is it time for a more simplified approach? Ultrasound Obstet Gynecol 2013; 41: 710–711. 22. Allen VM, Baskett TF, O’Connell CM, McKeen D, Allen AC. Maternal and perinatal outcomes with increasing duration of the second stage of labor. Obstet Gynecol 2009; 113: 1248–1258. 23. Pescetto G, De Cecco L, Pecorari D, Ragni N. In Ginecologia Ed Ostetricia, vol. 2. Universo: Milano, Italy, 2001; 1211.
SUPPORTING INFORMATION ON THE INTERNET The following supporting information may be found in the online version of this article: Table S1 Univariable and stepwise multivariable logistic regression analyses to identify parameters that have a significant association with active second stage length > 60 minutes in 71 patients at the beginning of active second stage (T1). Table S2 Demographic and clinical details in the study population of 74 women at the beginning of the active second stage of labor, stratified according to occiput position at delivery. Table S3 Sonographic data stratified according to occiput position at delivery.
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Sonographic pattern of fetal head descent: relationship with duration of active second stage of labor and occiput position at delivery T. GHI*, E. MARONI*, A. YOUSSEF*, A. M. MORSELLI-LABATE†, A. PACCAPELO†, E. MONTAGUTI*, N. RIZZO* and G. PILU* *Department of Obstetrics and Gynecology, Sant’Orsola-Malpighi Hospital, Alma Mater-University of Bologna, Bologna, Italy; †Department of Medical and Surgical Sciences, Alma Mater-University of Bologna, Bologna, Italy
K E Y W O R D S: intrapartum ultrasound; labor; persistent occiput posterior; second stage; three-dimensional
ABSTRACT Objectives The objectives of this study were firstly to assess the longitudinal changes of various sonographic parameters of fetal head progression in relation to length of active second stage of labor, and secondly to compare ultrasound findings obtained longitudinally among fetuses with persistent occiput posterior (OP) vs those with persistent occiput anterior (OA) position. Methods From a series of nulliparous low-risk women at term attending the labor ward of our university hospital, transperineal ultrasound volumes were prospectively acquired at the beginning of the active second stage (T1) and at 40-min intervals thereafter until delivery (T2, T3). Sonographic parameters were derived from offline analysis of each volume, including the angle of progression (AoP), progression distance (PD), head–symphysis distance (HSD), head direction (HD) and midline angle. These parameters were compared between patients who delivered within 60 min from the beginning of the active second stage of labor (early delivery) and those who remained undelivered by that time (late delivery). Fetal head position was determined from stored digital images of transabdominal examinations performed at the beginning of the active second stage. Comparison was performed between fetuses with OA and those with persistent OP position at delivery. Results Spontaneous vaginal delivery was achieved in 58 (81.7%) cases, whereas vacuum extraction and Cesarean section were performed in eight (11.3%) and five (7.0%) cases, respectively. Delivery was achieved within 60 min from the beginning of the active second stage in 44 (62.0%) patients. In the early vs late delivery groups, measurements of AoP, HSD and PD at T1 were significantly
different (AoP, 143.9 ± 20.5◦ vs 125.3 ± 15.0◦ , P < 0.001; HSD, 14.8 ± 4.5 mm vs 20.9 ± 5.8 mm, P < 0.001; PD, 44.0 ± 14.1 vs 35.0 ± 13.1 mm, P = 0.008). On logistic regression analysis of data obtained at T1, maternal body mass index, oxytocin administration, neonatal birth weight and HSD appeared to predict independently duration of the active second stage. Among fetuses delivering in the OP position (n = 10, 13.5%), Cesarean delivery was significantly more common than in those delivering in the OA position (n = 5 (50.0%) vs n = 2 (3.1%), P = 0.001). Women with persistent OP position compared with OA showed a significantly different AoP at T1 (122 ± 17◦ vs 138 ± 20◦ , P = 0.016), HD and HSD at T1 (HD, 112 ± 17 mm vs 86 ± 19 mm, P < 0.001; HSD, 16.5 ± 5.4 mm vs 22.8 ± 6.6 mm, P = 0.008) and at T2 (HD, 120 ± 16 vs 82 ± 27 mm, P = 0.008; HSD, 12.6 ± 3.4 mm vs 18.5 ± 5.4 mm, P = 0.038). Conclusions AoP, PD and HSD are significantly different between patients undergoing delivery before or after 60 min from the beginning of the active second stage of labor. Ultrasound parameters are among the significant predictors of duration of the active second stage. Moreover, in fetuses persisting in the OP position vs those delivering in the OA position, fetal head progression seems to differ at early phases of the active second stage. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
INTRODUCTION Prediction of vaginal delivery in a laboring woman is traditionally based upon assessment of progression of cervical dilatation and fetal head descent. When progression is poor, arrest of labor – currently the leading
Correspondence to: Dr T. Ghi, Obstetrics and Prenatal Medicine Unit, Sant’Orsola-Malpighi University Hospital, University of Bologna, Italy, Via Massarenti 13, 40138 Bologna, Italy (e-mail: [email protected]) Accepted: 22 January 2014
Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
ORIGINAL PAPER
Fetal head descent, second stage of labor and occiput position at delivery indication for primary Cesarean section in the USA – is diagnosed and obstetric intervention is needed1 . Extreme variability exists in the clinical definition of dystocia. In the active second stage, different criteria are used according to parity or epidural administration1 . A bulletin issued by a panel of experts states ‘If progress is made, the duration alone does not mandate delivery’1 . However some large studies have consistently shown that the longer the active second stage, the lower the chance of spontaneous vaginal delivery and the higher the risk of serious maternal or perinatal events2,3 . Fetuses with a persistent occiput posterior (OP) position in the second stage are at higher risk of dystocia or labor complications. In this group a higher risk of Cesarean section or need for operative vaginal delivery is consistently reported, and a globally increased incidence of maternal and perinatal complications is widely acknowledged4 – 7 . Ultrasonography has recently been used to assess fetal head progression during the second stage of labor8 – 16 , and sonographic data have been compared with digital findings12 – 15 . However, studies on sonographic evaluation of head descent have mostly focused on fetuses with occiput anterior (OA) position, while those with persistent OP position have been excluded or not assessed separately10 . The aims of this study were firstly to assess the longitudinal changes of various sonographic parameters of fetal head progression in relation to length of the active second stage of labor and secondly to compare ultrasound findings obtained longitudinally among fetuses with persistent OP vs those with persistent OA position.
SUBJECTS AND METHODS Transperineal ultrasound volumes were prospectively acquired from a non-consecutive series of nulliparous women attending the labor ward of our university hospital with uncomplicated singleton pregnancies at term (≥ 37 weeks) and with fetuses in cephalic presentation. Data from 71 women recruited between November 2010 and November 2011 were used for the longitudinal analysis of sonographic parameters. Data from these 71 women have been published previously16 . For comparison of occiput position, data from another three OP cases recruited up to September 2012 were included. Women were considered eligible regardless of whether labor was spontaneous or induced. Recruitment was carried out at the onset of labor when a trained investigator, with at least 3 years of experience in obstetric ultrasound, was available in the labor ward for the purposes of the study. Women were considered to be in the active second stage when they reached full cervical dilatation and began active pushing. Digital examination was performed before ultrasound scan to determine fetal head station and position. Ultrasonography was performed using a portable machine (Voluson i, GE Medical Systems, Zipf, Austria) equipped with a volumetric probe by one of the investigators (T.G.,
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E.M., A.Y., E.M. or G.P.), who was blinded to the findings on clinical examination. Ultrasound volume acquisition was carried out with an infrapubic or translabial approach in the absence of maternal pushing and uterine contractions, as described elsewhere12 . The woman’s bladder was kept empty by means of intermittent catheterization throughout the whole active second stage of labor, including during ultrasound examination. Both digital examination and ultrasound scan were performed at the beginning of the active second stage (T1) and at 40-min intervals thereafter (T2, T3) until delivery. All volumes were transferred to a personal computer equipped with dedicated software (4D view 9.0 and Sono-VCAD labor; GE Medical Systems) for offline analysis following delivery. Fetal head position at the beginning of the active second stage had not been prospectively assessed in these 71 women, and was retrospectively derived from digital images obtained by transabdominal and transperineal ultrasound and stored in the archive of the machine. In the extended study period, the fetal occiput position was prospectively checked by transabdominal ultrasound. The occiput position was labeled as anterior, posterior or transverse (right or left). The occiput position was defined as transverse when the midline angle was about 90◦ 11 . Fetal occiput position was visually determined at delivery (either vaginal or abdominal). Sonographic parameters obtained at 40-min intervals were compared between OA and OP fetuses. Volume analysis was performed after delivery and did not influence clinical management of labor by the attending physician, who was blinded to the sonographic findings. Patients were excluded from the study if they underwent Cesarean section or instrumental vaginal delivery in the second stage solely because of suspected fetal distress. For offline analysis, the volume was opened in the multiplanar mode in which the sagittal plane was displayed on Panel A and the axial and coronal planes on Panels B and C, respectively. Each volume was processed using the static-VCI algorithm in order to improve image resolution in the reconstructed planes12 . Volume alignment was obtained using the pubis and the urethra as reference points as previously described12 . Subsequently, the Sono-VCAD labor software was launched and, using the midsagittal plane, the following data were calculated: angle of progression (AoP; defined as the angle between the longitudinal axis of the pubic bone and a line joining the lowest edge of the pubis to the lowest convexity of the fetal skull)9 ; progression distance (PD; defined as the distance (mm) between the infrapubic line and the lowest part of the fetal skull)17 ; head–symphysis distance (HSD; defined as the distance between the lowest edge of the symphysis pubis and the nearest point of the fetal skull along the infrapubic line)16 ; and head direction (evaluated only for the occiput position analysis and defined as the angle between the infrapubic line and the major longitudinal axis of the fetal head)8 . The latter line is automatically generated by the software as the one
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perpendicular to the biparietal diameter. Switching from the sagittal to the axial plane, the midline angle (MLA; defined as the angle between the anteroposterior axis of the maternal pelvis and the head midline) was calculated11 . The study protocol was approved by the local ethics committee (No: 137/2010/O/Oss) and an informed consent form was signed at the onset of labor by each eligible patient. The study protocol conforms to the ethical guidelines of the ‘World Medical Association (WMA) Declaration of Helsinki – Ethical Principles for Medical Research Involving Human Subjects’ adopted by the 18th WMA General Assembly, Helsinki, Finland, June 1964 and amended by the 59th WMA General Assembly, Seoul, South Korea, October 2008.
Statistical analysis Data are reported as mean ± SD, median and range or frequencies. Data were compared between patients who delivered within 60 min from the beginning of the active second stage of labor (early delivery) and those who remained undelivered by that time (late delivery) by means of the Fisher’s exact, Kruskal–Wallis and Pearson chi-square tests. Comparisons between the two groups were made without taking into account the fetal occiput position at the beginning of the active second stage or at delivery. Receiver–operating characteristics (ROC) curves were constructed in order to estimate the accuracy of ultrasound parameters in predicting duration of the active second stage. The area under the ROC curve (AUC) was computed together with the 95% CI. The estimated ranges of best cut-off values were calculated by means of a maximum likelihood ratio method18 . Stepwise backward multivariable logistic regression analysis was applied in order to identify which variables independently predicted duration of the active second stage. In order to estimate duration of the active second stage according to ultrasound parameters, we used the Kaplan–Meier procedure, and the log-rank test for
trend was applied. In these analyses the ultrasound parameters were categorized according to quartile values (computed by using the data of the first ultrasound examination at the beginning of active maternal pushing and by applying the empirical-distribution-with-averaging method), and operative deliveries were considered as censored data. The SPSS version 13.0 for Windows statistical package (SPPS, Inc., Chicago, IL, USA) was used to analyze data and two-tailed P < 0.05 was considered statistically significant.
RESULTS Of the 71 initially recruited patients, 58 (81.7%) underwent spontaneous vaginal delivery, while vacuum extraction and Cesarean section was performed owing to dystocia in eight (11.3%) and five (7.0%) cases, respectively. The mean duration of the active second stage was 56.0 ± 40.2 min (median, 44 (range, 7–191)) min. Overall, 44 patients (62.0%) were delivered within 60 min from the beginning of the active second stage (early delivery group; mean duration of active second stage, 31.0 ± 13.4 min) while 27 (38.0%) remained undelivered by that time (late delivery group; mean duration of active second stage, 96.8 ± 35.7 min). A comparison of demographic and labor characteristics of these two groups is given in Table 1. The only statistically significant difference between the two groups was a greater birth weight in the late vs early delivery group (3654 ± 360 vs 3313 ± 398 g, P < 0.001). Other characteristics were similar between the groups, including occiput position at delivery and rate of epidural administration. The rate of operative delivery, including Cesarean section and vacuum extraction, was slightly higher in the late delivery group, although this difference was not statistically significant. Sonographic data obtained in the two groups are shown in Table 2. In the late vs early delivery group, the AoP
Table 1 Clinical details of study population of 71 women at beginning of active second stage of labor, according to its duration: < 60 min (early delivery) or > 60 min (late delivery) Parameter Maternal age (years) Body mass index (kg/m2 ) Gestational age at delivery (weeks) Birth weight (g) Oxytocin administration Epidural analgesia Spontaneous delivery Operative delivery Vacuum extraction Cesarean section Duration of labor (min)‡ Occiput position at delivery Anterior Posterior
Early delivery (n = 44)
Late delivery (n = 27)
P
31.0 ± 4.8; 32 (20–41) 27.8 ± 4.1; 27.3 (18.4–37.2) 39.5 ± 1.2; 39.6 (37.3–41.7) 3313 ± 398; 3242 (2450–4150) 25 (56.8) 24 (54.5) 39 (88.6) 5 (11.4) 4 (9.1) 1 (2.3) 233.5 ± 118.6; 225 (30–501)
31.4 ± 5.1; 32 (21–41) 26.7 ± 3.4; 25.9 (17.9–33.8) 39.4 ± 1.2; 39.4 (37.3–41.7) 3654 ± 360; 3625 (2740–4520) 21 (77.8) 17 (63.0) 19 (70.4) 8 (29.6) 4 (14.8) 4 (14.8) 375.7 ± 138.6; 367 (190–824)
0.647* 0.349* 0.652* < 0.001* 0.081† 0.622† 0.065†
40 (90.9) 4 (9.1)
24 (88.9) 3 (11.1)
< 0.001* 1.000†
Data are expressed as mean ± SD; median (range) or as n (%). *Kruskal–Wallis test. †Fisher’s exact test. ‡Duration of labor: time elapsed from beginning of labor (3–4-cm dilatation, effaced cervix, regular uterine contractions) to delivery.
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Table 2 Sonographic data at beginning of active second stage of labor (T1) and at 40-min intervals thereafter (T2, T3) in 71 women, according to duration of active second stage: < 60 min (early delivery) or > 60 min (late delivery) Variable/time point
Early delivery (n = 44)
Late delivery (n = 27)
P*
143.9 ± 20.5; 142.5 (102–213) 161.0 ± 8.5; 161 (155–167) —
125.3 ± 15.0; 124 (102–165) 144.4 ± 17.7; 142 (115–180) 145.6 ± 30.8; 135 (121–209)
< 0.001 0.179 —
44.0 ± 14.1; 45 (12–68) 55.5 ± 5.0; 55.5 (51–59) —
35.0 ± 13.1; 37 (11–64) 47.1 ± 12.7; 46 (18–69) 46.3 ± 18.3; 40 (30–83)
0.008 0.211 —
14.8 ± 4.5; 14 (6–33) 12.5 ± 3.5; 12.5 (10–15) —
20.9 ± 5.8; 21 (10–34) 13.4 ± 4.3; 12 (7–18) 12.3 ± 4.2; 12 (7–18)
< 0.001 0.889 —
34.4 ± 16.4; 29 (7–69) 12.5 ± 2.1; 12.5 (11–14) —
41.1 ± 28.9; 36 (0–127) 28.2 ± 20.0; 28 (1–101) 25.3 ± 10.0; 26 (13–38)
0.445 0.138 —
◦
Angle of progression ( ) T1 (n = 44 vs n = 27) T2 (n = 2 vs n = 25) T3 (n = 0 vs n = 7) Progression distance (mm) T1 (n = 44 vs n = 27) T2 (n = 2 vs n = 25) T3 (n = 0 vs n = 7) Head–symphysis distance (mm) T1 (n = 44 vs n = 27) T2 (n = 2 vs n = 25) T3 (n = 0 vs n = 7) Midline angle (◦ ) T1 (n = 44 vs n = 27) T2 (n = 2 vs n = 25) T3 (n = 0 vs n = 7)
Data are expressed as mean ± SD and median (range). *Kruskal–Wallis test.
1.0 0.9 0.8
Sensitivity
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1 – Specificity
Figure 1 Receiver–operating characteristics curves for angle of ), progression distance ( ) and progression ( ) at onset of active second stage of head–symphysis distance ( labor in a cohort of 71 women, showing accuracy of these ultrasonographic parameters in discriminating late (> 60 min) from early (< 60 min) delivery.
and PD were significantly smaller at T1 whereas the HSD was significantly greater in the former group at the same time frame. No significant difference in the MLA was found at any time. At T2, no difference was found in any sonographic parameter; however, of those patients assessed at this time point only two delivered within an hour of the start of the active second stage, severely limiting the power of statistical tests. In order to evaluate the accuracy of ultrasound parameters in the prediction of late delivery, ROC curves of the parameters that were found to be statistically significantly different between the two groups were constructed (Figure 1). The AUCs are reported in Table 3 together with sensitivities, specificities and predictive values obtained by subdividing the study population according to the best cut-off values. Kaplan–Meier analysis was applied in order to estimate duration of the spontaneous active second stage in the whole population according to the distribution of the sonographic parameters. Greater values of AoP and PD at the beginning of the active second stage correlated with a shorter time to delivery, while a direct relationship was found between HSD and duration of active second stage (Figure 2 and Table 4). The relationship between clinical and sonographic parameters and late delivery was analyzed by means
Table 3 Summary statistics of receiver–operating characteristics (ROC) curve analysis for angle of progression (AoP), progression distance (PD) and head–symphysis distance (HSD) evaluated in 71 patients at beginning of active second stage of labor in predicting late delivery (> 60 min)
Variable AoP PD HSD
Area under ROC curve (95% CI)
Estimated best cut-off range
Sensitivity (n/N (%))
Specificity (n/N (%))
PPV (n/N (%))
NPV (n/N (%))
0.777 (0.666–0.888) 0.688 (0.563–0.814) 0.816 (0.709–0.781)
139–142◦ 38–39 mm 19–20 mm
25/27 (92.6) 20/27 (74.1) 16/27 (59.3)
24/44 (54.5) 29/44 (65.9) 42/44 (95.5)
25/45 (55.6) 20/35 (57.1) 16/18 (88.9)
24/26 (92.3) 29/36 (80.6) 42/53 (79.2)
NPV, negative predictive value; PPV, positive predictive value.
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Proportion of pregnancies undelivered
(a)
Table 4 Mean duration of active second stage of labor estimated by Kaplan–Meier analysis performed for angle of progression, progression distance and head–symphysis distance in 71 patients at beginning of active stage, stratified by quartiles of each variable
1.0
0.8
Parameter 0.6
0.4
0.2
0.0 0
50
100
150
200
Duration of second stage of labor (min)
Proportion of pregnancies undelivered
(b)
1.0
95% CI (min)*
96.3 ± 13.7 62.6 ± 10.7 50.2 ± 7.5 37.6 ± 5.1
69.4–123.2 41.7–83.5 35.4–64.9 27.6–47.6
88.5 ± 16.6 73.6 ± 10.3 52.4 ± 7.8 38.4 ± 4.5
56.0–121.0 53.4–93.7 37.1–67.6 29.5–47.3
39.8 ± 4.6 37.7 ± 4.6 63.2 ± 10.8 124.8 ± 13.2
30.9–48.8 28.7–46.7 42.0–84.5 99.0–150.6
P† < 0.001
0.001
< 0.001
*95% CI of estimated mean length of active second stage of labor. †Log-rank test for trend. 0.8
0.6
0.4
0.2
0.0 0
50
100
150
200
Duration of second stage of labor (min) (c) 1.0 Proportion of pregnancies undelivered
Angle of progression 1st quartile (≤ 122◦ ) 2nd quartile (123–134◦ ) 3rd quartile (135–150◦ ) 4th quartile (> 150◦ ) Progression distance 1st quartile (≤ 30 mm) 2nd quartile (31–39 mm) 3rd quartile (40–52 mm) 4th quartile (> 52 mm) Head–symphysis distance 1st quartile (≤ 12 mm) 2nd quartile (13–17 mm) 3rd quartile (18–20 mm) 4th quartile (> 20 mm)
Mean ± SE (min)
0.8
0.6
0.4
0.2
0.0 0
50
100
150
200
Duration of second stage of labor (min)
Figure 2 Kaplan–Meier analysis showing time to delivery in relation to angle of progression (a), progression distance (b) and head–symphysis distance (c) at beginning of active second stage of labor. Data are stratified according to the quartiles of each variable: , 1st quartile; , 2nd quartile; , 3rd quartile; , 4th quartile.
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of univariable and multivariable logistic regression (Table S1). Duration of the active second stage was significantly related to all sonographic parameters, apart from MLA, at the beginning of the active second stage. Multivariable analysis showed that, at the beginning of the active second stage, HSD together with maternal body mass index, oxytocin administration and neonatal birth weight appeared to predict independently duration of the active second stage. Demographic details and labor outcome according to fetal occiput position at delivery are summarized in Table S2. Patient characteristics were similar between the two groups, including the rate of scheduled epidural administration. Of the 10 fetuses delivered in a persistent OP position, the rate of Cesarean section was much higher than in those delivered in the OA position (n = 5 (50.0%) vs n = 2 (3.1%), P < 0.001), while rates of vacuum extraction were comparable (n = 1 (10%) vs n = 8 (12.5%), P = 0.650). Sonographic data obtained in the two groups are reported in Table S3. Women with a persistent OP position showed a significantly smaller AoP at T1 than did those with an OA position (122 ± 17◦ vs 138 ± 20◦ , P = 0.016). Furthermore, HD and HSD were significantly different in the two groups at T1 (HD, 112 ± 17 mm vs 86 ± 19 mm, P < 0.001; HSD, 16.5 ± 5.4 mm vs 22.8 ± 6.6 mm, P = 0.008) and T2 (HD, 120 ± 16 mm vs 82 ± 27 mm, P = 0.008; HSD, 12.6 ± 3.4 mm vs 18.5 ± 5.4 mm, P = 0.038). No significant differences were observed for PD and MLA. Only one case in the OP position remained undelivered at T3, which did not allow comparison of sonographic data with fetuses in the OA position at this time point. However, in this case the fetal head showed an upward direction, and both AoP and HSD were similar to values obtained from cases of OA.
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OA position
(a)
(b)
(c)
(b)
(c)
OP position
(a)
Figure 3 Schematic representation of fetal head progression through maternal pelvis in occiput anterior (OA) and occiput posterior (OP) fetuses. In vertex-presenting fetuses, head descent converts from downward at inlet (a) to horizontal at midpelvis (b) to upward at outlet (c). OP fetuses maintain a downward direction with respect to the pubic bone from inlet to midpelvis (a,b) and only after passing the ischial spines do they abruptly twist up towards the outlet (c) only in those cases that are delivered vaginally.
DISCUSSION
Figure 4 Sonographic demonstration of head descent in the birth canal in occiput anterior (OA) and occiput posterior (OP) fetuses. At the beginning of active second stage (T1), in OP fetuses the head was directed more downward and the head–symphysis distance (HSD) appeared greater than that of OA fetuses. After 40 min (T2), among the OP group the fetal head maintained a downward direction and a significantly greater HSD was still noted.
Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
Our study provides original data on the longitudinal changes of several ultrasound parameters during the active second stage of labor; we found a significant correlation between ultrasound findings and duration of the active second stage. Multivariable logistic regression analysis demonstrated that sonographic findings were significant predictors of the active second stage length together with birth weight, maternal body mass index and oxytocin augmentation. This is in agreement with previous studies by Barbera et al.9 , who first reported that the narrower the angle of progression at the beginning of the active second stage, the longer is the time to delivery. Our data suggest that a similar correlation also exists with other sonographic measurements, including HSD and PD. We suggest that this is a valuable observation, because at present it is uncertain which is the most convenient ultrasound parameter for evaluating descent of the fetal head19,20 . Many advocate the use of a simple approach to aid operators with limited experience of diagnostic ultrasound21 . For this reason, we have previously proposed the use of HSD, a highly reproducible linear measurement15 . HSD demonstrates a strong correlation with the duration of the active second stage, and is no more difficult to obtain than is AoP. As shown in Table 4, if HSD is greater than 20 mm at the beginning of the active second stage, the length of this stage is likely to exceed 60 min, with a mean duration of 1.5 h. It is well established that a prolonged second stage is associated with a lower chance of spontaneous vaginal
Ultrasound Obstet Gynecol 2014; 44: 82–89.
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delivery and an increased risk of maternal and fetal complications2,3,22 . Prediction of the time to delivery would be useful in many different clinical situations, particularly those involving abnormal fetal electronic monitoring and patients with a reduced tolerance to physical exertion because of cardiac disease or other disorders. Our study also showed that there is a measurable difference in sonographic findings of head descent when the occiput is posterior rather than anterior. Fetuses with OA follow the curved path of the birth canal (Figure 3) and this results in a progressive increase in the AoP and PD, with a simultaneous decrease in HSD. On the other hand, with OP the head descends maintaining a downward direction for a much longer time, until the forehead has passed the pubic bone. This results initially in a smaller AoP and a greater HSD than in fetuses with OA presentation. While the head descends the AoP increases slowly while the HSD remains constant or increases. Among the OP fetuses of our series smaller values of both AoP and HD and a greater HSD were indeed documented by ultrasound up to 40 min from the beginning of the active second stage (Figure 4). A more horizontal or downward fetal HD with respect to the pubic bone has been sonographically witnessed by others among fetuses with a persistent OP position in the active second stage8,14 . This confirms that the mechanism of vaginal delivery of OP fetuses requires an increased distension of the perineum to accommodate a greater degree of downward descent of the fetal head, until the forehead has completely passed the pubic bone23 . At this time, flexion of the head becomes possible and sonography demonstrates a marked decrease in HSD. Owing to this upward change of fetal head progression, the descent path of OP fetuses is likely to become similar to that of OA fetuses in the later phases of the second stage. However of the fetuses delivered vaginally in persistent OP position, only one case of this series remained undelivered after 80 min, preventing further comparison of sonographic measurements with fetuses delivered in the OA position. Interestingly the PD does not seem to vary significantly between OP and OA cases, and this suggests that it is not the depth but rather the direction of the fetal head descent that is affected in the former group, leading to an increased chance of dystocia and need for Cesarean section and possibly to the increased rate of failure in instrumental vaginal delivery. On the other hand, the MLA is comparable in OP and OA fetuses. This seems to indicate that OP fetuses engage along the oblique diameter of the pelvic inlet and undergo a movement of internal rotation at the midpelvis similarly to OA fetuses. We acknowledge several limitations of our study. The most important one is the limited number of cases. We aimed to obtain longitudinal evaluations, but the longer the interval from the beginning of the active second stage, the smaller the number of patients who remained undelivered and were available for comparison. We believe that this is the most likely explanation for the absence of significant differences in sonographic findings in the advanced active second stage. The lack of a significant
Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
difference in the MLA in patients who delivered early vs those who delivered late is almost certainly due to the fact that head rotation only occurs at an advanced stage of fetal head descent. The lack of a significant difference in the rate of operative delivery between patients who delivered early vs those who delivered late is also probably a consequence of the small numbers in the study. In conclusion, our study has shown that sonographic findings predict the duration of the active second stage of labor. We have also described the sonographic appearance of the pattern of head descent of fetuses with OP presentation, and this may prove useful in the future to set a standard to diagnose abnormal labor, which is very frequent in these cases. At the moment the use of ultrasound in labor is limited to the research setting. Our study may represent a step towards the introduction of this tool in clinical practice.
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SUPPORTING INFORMATION ON THE INTERNET The following supporting information may be found in the online version of this article: Table S1 Univariable and stepwise multivariable logistic regression analyses to identify parameters that have a significant association with active second stage length > 60 minutes in 71 patients at the beginning of active second stage (T1). Table S2 Demographic and clinical details in the study population of 74 women at the beginning of the active second stage of labor, stratified according to occiput position at delivery. Table S3 Sonographic data stratified according to occiput position at delivery.
Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd.
Ultrasound Obstet Gynecol 2014; 44: 82–89.
