The Journal of Maternal-Fetal & Neonatal Medicine
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Ultrasound assessment of fetal head circumference at the onset of labor as a predictor of operative delivery Poh Vei Ooi, Meenakshi Ramphul, Soha Said, Gerard Burke, Mairead M. Kennelly & Deirdre J. Murphy To cite this article: Poh Vei Ooi, Meenakshi Ramphul, Soha Said, Gerard Burke, Mairead M. Kennelly & Deirdre J. Murphy (2015) Ultrasound assessment of fetal head circumference at the onset of labor as a predictor of operative delivery, The Journal of Maternal-Fetal & Neonatal Medicine, 28:18, 2182-2186, DOI: 10.3109/14767058.2014.980810 To link to this article: http://dx.doi.org/10.3109/14767058.2014.980810
Accepted author version posted online: 03 Nov 2014. Published online: 14 Nov 2014. Submit your article to this journal
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Date: 06 November 2015, At: 05:04
http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, 2015; 28(18): 2182–2186 ! 2014 Informa UK Ltd. DOI: 10.3109/14767058.2014.980810
ORIGINAL ARTICLE
Ultrasound assessment of fetal head circumference at the onset of labor as a predictor of operative delivery Poh Vei Ooi1,2, Meenakshi Ramphul2,3, Soha Said1,4, Gerard Burke1,4, Mairead M. Kennelly2, and Deirdre J. Murphy2,3 University Maternity Hospital, Limerick, Republic of Ireland, 2Department of Obstetrics and Gynaecology, Trinity College, Dublin, Republic of Ireland, 3Coombe Women and Infants University Hospital, Dublin, Republic of Ireland, and 4Department of Obstetrics and Gynaecology, Graduate Entry Medical School, University of Limerick, Limerick, Republic of Ireland
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1
Abstract
Keywords
Objective: This study sought to determine whether ultrasound assessment of fetal head circumference (FHC) at the onset of labor can predict the likelihood of operative delivery. Methods: We performed a prospective cohort study of 200 nulliparous women with singleton, cephalic, term pregnancies in an Irish Maternity Hospital. Transabdominal ultrasound assessment of FHC was performed when spontaneous labor was diagnosed or immediately prior to induction. Odds ratios for operative delivery (instrumental delivery or cesarean section) and maternal and neonatal morbidity were calculated using logistic regression with FHC categorized at a 350-mm cut-off (90th percentile). Results: Ultrasound assessment of FHC at the onset of labor was highly correlated with postdelivery neonatal head circumference (NHC) (Pearson’s correlation coefficient 0.74), suggesting that it can be measured reliably. FHC 350 mm was associated with more than twice the risk of any operative delivery (OR 2.5, 95% CI 1.0–6.2) and a two-fold increased risk of cesarean section for dystocia (OR 2.0, 95% CI 1.0–4.3). Differences in maternal and neonatal morbidity were not statistically significant. Conclusion: These preliminary data suggest that ultrasound assessment of FHC at the onset of labor may be useful in identifying women at greater risk of intrapartum intervention and warrant further research.
Cesarean section, fetal head circumference, instrumental delivery, labor, ultrasound.
Introduction Every year, more than 10 000 women in Ireland give birth by instrumental delivery [1]. Indications for forceps and vacuum include prolonged second stage of labor, suspected fetal compromise and medical disorders that warrant shortening of the active second stage [2–4]. In cases where cephalopelvic disproportion is suspected or instrumental delivery fails, cesarean section plays an essential role [5]. Operative deliveries in the second stage of labor (both instrumental delivery and cesarean section) are associated with significant maternal and perinatal morbidity and mortality, and also with psychological morbidity [5–7]. Forceps delivery and vacuum extraction are associated with maternal urinary dysfunction and perineal trauma including anal sphincter injuries, while perinatal trauma includes scalp laceration, cephalhematoma, retinal hemorrhage, facial nerve and cranial injuries [6–8]. Address for correspondence: Professor Deirdre J. Murphy, Academic Department of Obstetrics & Gynaecology, Trinity College, University of Dublin, Dublin, Republic of Ireland & Coombe Women & Infants University Hospital, Cork Street, Dublin 8, Republic of Ireland. Tel: +353-1-4085200. Direct: +353-1-4082126. Fax: +353-1-4531614. E-mail: [email protected]
History Received 11 August 2014 Revised 19 October 2014 Accepted 22 October 2014 Published online 14 November 2014
Morbidity increases when multiple instruments are used [9,10]. Cesarean section at full dilatation is associated with major maternal hemorrhage, prolonged hospital stay and an increase in neonatal admissions to the intensive care unit [5,7]. Attempts to identify women at highest risk of cephalopelvic disproportion have concluded that neither X-ray, computed tomography or magnetic resonance imaging pelvimetry have a proven value in labor management or clinical outcomes [11–13]. Research evaluating fetal factors in operative delivery has focused mainly on estimated fetal weight to predict macrosomia. However, ultrasound estimation of fetal weight has been shown to differ from actual birth weight by as much as 20%, and identifying suspected fetal macrosomia, other than for diabetic pregnancies, has not been shown to improve labor outcomes [14–15]. A further challenge relates to the timing of ultrasound assessment as several weeks may elapse between the time of antenatal assessment and the onset of labor. The role of ultrasound in labor warrants consideration [16]. Several studies have reported an association between increased neonatal head circumference (NHC) and prolonged second stage of labor, instrumental delivery and cesarean section [17–20]. However, NHC can only be obtained
Ultrasound assessment of FHC
DOI: 10.3109/14767058.2014.980810
following delivery and has no predictive value for interventions in labor. Ultrasound assessment of the fetal head position immediately prior to instrumental delivery has been shown to be feasible and to markedly reduce the incidence of incorrect diagnosis of the fetal head position [21–23]. Fetal head circumference (FHC) is a parameter that is familiar to most novice sonographers and would be relatively simple and attainable in a labor room setting. This study set out to investigate whether ultrasound assessment of the FHC at the onset of labor can be reliably ascertained compared to NHC, and whether it could potentially have a predictive role in identifying women at increased risk of operative delivery by forceps, vacuum or cesarean section.
Methods
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Validation study Prior to commencing the prospective cohort study, a validation study was performed aiming to ascertain the validity and reliability of ultrasound assessment of fetal head measurements as recorded by a novice research sonographer in comparison with an expert sonographer. A total of 35 participants consented to an intrapartum ultrasound scan. All participants were at least 37 weeks gestation and 80% were in the active first stage of labor. Three scan images were taken for each participant, and the results were averaged. Optimal ultrasound measurements of FHC and biparietal diameter (BPD) were obtained in 28 participants (80%), and the remainder was sub-optimal. We considered the FHC and BPD to be optimal when a clear outline of the entire fetal skull was obtained, and the landmarks (the cavum septum pellucidum, thallamus and choroid plexus in the atrium of the lateral ventricles) were visualized. Transabdominal measurements of the FHC were measured by the novice sonographer and the expert, who is a sub-specialist in fetal and maternal medicine, not more than 10 min apart, recorded separately and later analyzed using intraclass correlation coefficients. Bland–Altman plots were constructed to assess level of agreement between novice and expert measurements. A very high correlation between ultrasound measurements of the FHC performed by the novice and expert was demonstrated with a significant intra-class correlation coefficient (ICC) of 0.78, supporting the validity of novice sonographic measurements (inter-observer reliability). High intra-observer reliability was also shown, suggesting good reproducibility not only for expert, but also for novice FHC measurements (ICC 0.88 and 0.83, respectively). Prospective cohort study A prospective cohort study was followed, which was carried out between September 2011 and June 2012 in a regional maternity hospital with over 5000 deliveries annually. Participants included were nulliparous women at term, defined as at least 37 weeks gestation, with singleton cephalic pregnancies aiming to deliver vaginally. Women excluded were those less than 18 years old, who had limited command of the English language, deemed incapable of providing informed consent by the midwife in charge of her care, who had inadequate pain relief or who had systemic opiates in the
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previous 4 h. Potential participants admitted for induction of labor or with a spontaneous onset of labor were approached, and written informed consent was sought if they satisfied the inclusion criteria. We confined the study to nulliparous women in order to increase the probability of operative delivery and therefore the power of the study to detect a statistical difference. Many of the women approached were booked for induction of labor in keeping with the criteria imposed by the research ethics committee in terms of allowing women an appropriate time interval to consider study participation. Participants received a transabdominal ultrasound scan measuring FHC (FHC) at the onset of induced and spontaneous labors, performed by a single research sonographer (as described above). The FHC images were categorized as optimal, satisfactory, poor or unattainable. Subsequent details of labor outcome as well as NHC post-delivery were obtained from maternal and neonatal medical records and recorded in a case report form. The primary outcome of interest was a combined category termed operative delivery that included all instrumental deliveries or cesarean sections. Secondary outcomes included prolonged first and second stage of labor, sequential use of instruments, indication for cesarean section, obstetric anal sphincter injury, primary postpartum hemorrhage (PPH), neonatal trauma and admission to the neonatal unit. The analyses were performed using the Predictive Analytics Software Statistics (PASW version 17). Descriptive statistics were used to characterize the patient population. Primary analyses evaluated the relationship between FHC and operative delivery according to a pre-specified cut-off threshold set at 350 mm based on the 90th percentile for FHC at 38–39 weeks’ gestation on standard fetal growth charts [24,25]. The cut-off for NHC was determined to be 370 mm based on the 90th percentile for UK-WHO growth charts [26]. It is important to note that the FHC is based on an ellipse drawn around the bony skull of the fetal head, and the NHC is a measurement that includes the scalp and subcutaneous tissues and soft tissue swelling as the measurements are taken shortly following birth, hence the difference in the absolute values. These cut-off values were consistent with the 90th percentile for retrospective data obtained by our research group [17]. Results are presented as proportions, odds ratio and 95% confidence intervals, with a two-tailed level of significance (p50.05) ascertained using chi-squared analysis. Secondary analyses of maternal and neonatal morbidity outcomes were performed in the same way. The relationship between individual FHC and the corresponding NHC was analyzed using Pearson’s correlation coefficient with significance calculated using the student’s t test. A receiver operating characteristic (ROC) curve was produced to assess the predictive probability of FHC as a measure for operative delivery (combined instrumental delivery and cesarean section). The area under the curve (AUC) was calculated with 95% confidence intervals.
Results A total of 200 women consented to participate in the study out of 210 eligible women approached. Demographic and obstetric characteristics of the cohort are presented in Table 1,
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Table 1. Characteristics of study population and descriptive statistics for fetal head circumference, biparietal diameter and neonatal head circumference. Characteristics
Mean
N ¼ 200 Maternal age (years) Maternal BMI (kg/m2) Gestational age at delivery (weeks) Cervical dilatation at scan (cm) Birth weight (g) FHC (mm) BPD (mm) NHC (mm)
SD
Median
Min
Max
28.2 25.3 40.0
5.7 5.1 1.1
28.0 24.0 39.9
18.0 16.0 37.3
41.0 40.0 41.7
2.7
1.7
2.0
1.0
10.0
3551.8 339.0 94.1 353.6
451.7 12.7 4.3 14.4
3625.0 340.0 94.0 355.0
2230.0 307.0 77.0 320.0
4750.0 373.0 103.0 390.0
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SD: standard deviation; BMI: body mass index; HC: head circumference; BPD: biparietal diameter; FHC: fetal head circumference; NHC: neonatal head circumference
Table 2. Overall and image-quality adjusted correlation between fetal head circumference and neonatal head circumference.
Characteristics
Mean
Overall (n ¼ 200) Fetal HC 339.0 Neonatal HC 353.6 High quality (n ¼ 170) Fetal HC 339.8 Neonatal HC 353.6
SD
Standard error mean
12.7 14.4 12.4 14.4
Pearson’s correlation
p
0.9 1.0
0.735
0.0001
1.0 1.0
0.813
0.0001
SD: standard deviation; HC: head circumference. High quality: Optimal or satisfactory images obtained.
along with the descriptive statistics for sonographic FHC, BPD and NHC measured post-delivery. All patients were nulliparous, in the first stage of labor and 77% had labor induced. All transabdominal ultrasound assessments were performed within 24 h of delivery. The FHC images were optimal or satisfactory in 170 cases. Spontaneous vaginal delivery occurred in 28% of women, while rates of instrumental delivery and cesarean section were 39 and 34%, respectively. Of the women who had an instrumental delivery, six (3%) involved the use of sequential instruments. For the majority of cases, the instrument used was a disposable vacuum (60%), followed by a metal cup vacuum (23%) and non-rotational forceps (17%). There was a high correlation between sonographic FHC and NHC post-delivery (Pearson’s 0.74, p50.01). Table 2 reports a comparison of the degree of correlation before and after adjusting for image quality, where only high-quality images (optimal or satisfactory) were included (Pearson’s correlation 0.81, p50.01). A ROC curve was produced which demonstrated a significant predictive probability of FHC as a measure for operative delivery; area under curve 0.64 (95% CI 0.54–0.73). Table 3 reports a comparison of labor outcomes between groups for both sonographic FHC and NHC post-delivery. FHC at or above 350 mm was associated with an increased risk of operative delivery (combined instrumental delivery and cesarean section) (OR 2.5, CI 1.04–6.2, p ¼ 0.04).
The risk of cesarean section for dystocia was increased twofold (OR 2.0, CI 1.0–4.2, p ¼ 0.08). NHC at or above 370 mm was associated with an increased risk of instrumental delivery (OR 2.2 CI 1.1–4.5, p ¼ 0.03), but the association with combined operative delivery did not reach statistical significance.
Discussion FHC at the onset of labor was found to be a reliable measure demonstrating high correlation with NHC. NHC has been associated with an increased risk of operative delivery, and similarly, we established that a FHC threshold of 350 mm was associated with a two-fold increased risk of combined operative delivery. The AUC calculated from the ROC graph showed that the predictive potential of FHC as a screening tool for operative delivery in labor is promising and warrants further research. The initial validation study confirmed the accuracy of ultrasound measurements of FHC performed by a novice sonographer compared to an expert and verified the reproducibility of these measures. All of the ultrasound measurements in the prospective cohort study were performed by the same operator, thus ensuring methodological consistency. A deeply engaged fetal head was found in 14% of participants, contributing to difficulties in achieving the precise plane for sonographic FHC measurement, and these images were considered sub-optimal. Even so, analyses with and without sub-optimal images yielded very similar results. Random error was minimized by obtaining and averaging several measurements for each participant in keeping with standard practice for routine antenatal ultrasonography. Further subclassification of labor outcome into sequential instrumental delivery, failed instrumental delivery and obstetric anal sphincter injury resulted in small subgroups thereby limiting statistical analysis. We selected a higher risk population of nulliparous women, many of whom were induced and, while this increased statistical power, the results would not be generalisable to parous women with previous vaginal deliveries. This work should be viewed as preliminary and warrants replication in other settings and populations. A much larger sample size would be required to allow for testing of multiple associations. Comparison with existing literature Several studies have investigated the relationship between ‘‘fetal’’ head circumference and labor outcomes but, in fact, rely on newborn head circumference as a proxy for true FHC. A retrospective study analyzing singleton nulliparous cephalic pregnancies reported that an increased mean duration of labor and a longer second stage of labor were significantly associated with NHC of 370 mm and above [17]. Elvander et al. reported that data from singleton nulliparous deliveries over a 10-year period showing evidence that increasing NHC conferred significantly higher odds for instrumental deliveries as well as cesarean sections [19]. Mujugira et al. had similar findings in a multi-ethnic population [20]. Ayinde et al. examined singleton cephalic nulliparous and multiparous pregnancies and found that the cesarean delivery rate was
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Table 3. Labor outcome according to fetal and neonatal head circumference. Fetal HC* (mm)
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Characteristics 1st Stage 410 hrs 2nd Stage 42 hrs Total labor 412 hrs Operative delivery Total instrumental delivery Single instrument Sequential instruments Total cesarean section Dystocia Fetal distress Failed instrumental Postnatal maternal complication (all) 1 PPH Neonatal trauma Admission to SCBU Perineal trauma
5350 n ¼ 128 (%) 32 38 28 85 43 39 4 42 26 16 0 29 10 43 21 68
(25) (30) (23) (66) (34) (31) (3) (33) (20) (13) (0) (23) (8) (34) (16) (53)
350 n ¼ 42 (%) 11 14 9 35 17 15 2 19 14 4 1 14 6 16 8 21
(26) (33) (21) (83) (41) (36) (5) (45) (33) (10) (2) (33) (14) (38) (19) (50)
Neonatal HC (mm) FHC 350 mm OR (95% CI)
p
1.1 1.2 0.9 2.5 1.3 1.3 1.6 1.7 2.0 0.7
(0.5–2.7) (0.6–4.6) (0.4–2.5) (1.0–6.2) (0.7–2.8) (0.7–2.6) (0.3–8.8) (0.8–3.4) (1.0–4.3) (0.2–2.3)
0.65 0.19 0.91 0.04 0.42 0.53 0.62 0.15 0.08 0.61
1.7 1.4 1.2 1.2 0.7
(0.8–3.7) (0.4–5.3) (0.6–2.5) (0.5–3.0) (0.4–1.5)
0.17 0.59 0.60 0.69 0.37
5370 n ¼ 163 (%) 42 53 35 113 57 54 3 56 38 17 1 37 14 56 26 88
(27) (49) (23) (69) (35) (33) (2) (34) (23) (10) (1) (23) (9) (34) (16) (54)
370 n ¼ 37 (%) 11 14 10 31 20 17 3 11 8 3 0 13 6 19 7 22
(31) (52) (28) (84) (54) (46) (8) (30) (22) (8) (0) (53) (16) (51) (19) (59)
NHC 370 mm OR (95% CI)
P
1.2 1.1 1.3 2.3 2.2 1.7 4.7 0.8 0.9 0.8
(0.5–2.6) (0.5–2.6) (0.6–2.9) (0.9–5.8) (1.1–4.5) (0.8–3.5) (0.9–24.3) (0.4–1.8) (0.4–2.1) (0.2–2.7)
0.69 0.76 0.58 0.08 0.03 0.14 0.04 0.64 0.77 0.67
1.9 2.1 2.0 1.2 1.5
(0.9–4.0) (0.7–5.8) (1.0–4.1) (0.5–3.1) (0.7–3.1)
0.12 0.16 0.05 0.66 0.34
*Fetal HC based on 170 cases with optimal or satisfactory images. HC: head circumference; CI: confidence interval; hrs: hours; 1 PPH: primary postpartum hemorrhage; SCBU: special care baby unit; Operative Delivery: total instrumental delivery and caesarean section; Perineal trauma: 2nd + 3rd degree tear.
significantly higher only in nulliparous pregnancies with NHC measuring 370 mm and above [18]. The novel aspect of our study was the finding of an association between antenatally determined FHC and operative delivery, and a particularly strong association with cesarean section for dystocia. The advantage of this approach is that the information can be ascertained reliably at the onset of labor. Unlike studies exploring the association between estimated fetal weight, actual birth weight and delivery outcomes [14], we found a very strong correlation between FHC and NHC performed shortly following delivery. On average FHC measurements were 15 mm less than NHC measurements which is to be expected given that ultrasound measurement of FHC is based on the bony skull, and neonatal measurement is based on the occipitofrontal circumference including the infants scalp and subcutaneous tissues. Mathematically, the 15-mm difference equates to a 2.5-mm thickness of the soft tissues. We could have evaluated each individual FHC measurement by percentile; however, we choose a cut-off approach based on the 90th percentile at full term for two reasons. Firstly, this approach replicated the previous studies on NHC and allowed direct comparisons to be made, and secondly the choice of an easy to recall cut-off would facilitate interpretation and application of scan findings in the pressurized labor room environment. Operative delivery, particularly in the second stage of labor is a disappointing outcome for laboring women, as well as being associated with increased maternal and perinatal morbidity and implications for subsequent deliveries [5,27]. The ability to identify women at higher risk of operative intervention from the time of admission to the labor ward could have important implications for labor management, use of senior support and decisions on how to approach instrumental delivery. The potential downside of admission ultrasound is that it could introduce negativity at an early stage of labor in relation to the woman’s prospect for an uncomplicated spontaneous vaginal delivery. Clearly, intrapartum
ultrasonography should only be used as a guide alongside the analytical skills and experience of the obstetrician and midwife, as absolute reliance on the predictive ability of labor FHC could adversely affect the threshold for potentially unnecessary cesarean sections.
Conclusions FHC correlated closely with NHC and had a moderate predictive value for operative delivery. An FHC at or above 350 mm at the onset of labor was associated with more than twice the combined risk of instrumental delivery or cesarean section. Further large-scale population-based studies are required to validate these findings. An appropriately powered randomized controlled trial would be required to establish whether routine ultrasonographic assessment of FHC at the onset of labor has the potential to reduce adverse delivery outcomes.
Acknowledgements We would like to thank the obstetricians and midwives for their collaboration as well as the women attending the University Maternity Hospital Limerick who participated in the study.
Declaration of interest The authors acknowledge the financial support from the Health Research Board of Ireland and have no conflicts of interest to declare. We have no conflict of interest to declare. GB and DJM had the original idea for the study. DJM obtained funding and supervised the study, analysis of data and helped draft the manuscript. GB, MK and SS were responsible for validation of sonographic parameters. MR was responsible for classification and verification of image quality. PVO collected the data, carried out the analyses and drafted the manuscript. All authors reviewed and revised the
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manuscript. This study received the ethical approval of the ethics committee of the HSE West University Hospitals Group, Limerick.
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References 1. Consumer Guide to Maternity Services in Ireland [Internet]. Ireland 2010. Available from: http://www.bump2babe.ie/column/N/statistics/ [last accessed: 15 February 2013]. 2. Royal College of Obstetricians and Gynaecologists. Operative vaginal delivery. Greentop Guideline No. 26. London: RCOG; 2011. 3. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin 17. Operative vaginal delivery. Washington, DC: ACOG; 2000. 4. Clinical Practice Obstetrics Committee Society of Obstetricians and Gynecologists Canada. Guidelines for operative vaginal birth. SOGC Clinical Practice Guidelines No. 148. Ottawa, ON: SOGC; 2004. 5. Murphy DJ, Liebling RE, Verity L, et al. Early maternal and neonatal morbidity associated with operative delivery in second stage of labour: a cohort study. Lancet 2001;358:1203–7. 6. Towner D, Castro MA, Eby-Wilkens E, Gilbert WM. Effect of mode of delivery in nulliparous women on neonatal intracranial injury. N Engl J Med 1999;341:1709–14. 7. Spencer, C, Murphy DJ, Bewley S. Caesarean section in the second stage of labour. BMJ 2006;333:613–14. 8. Macleod M, Goyder K, Howarth L, et al. Morbidity experienced by women before and after operative vaginal delivery: prospective cohort study nested within a two-centre randomised controlled trial of restrictive versus routine use of episiotomy. BJOG 2013;120: 1020–6. 9. Murphy DJ, Liebling RE, Patel R, et al. Cohort study of operative delivery in the second stage of labour and standard of obstetric care. BJOG 2003;110:610–15. 10. Murphy DJ, Macleod M, Bahl R, Strachan B. A cohort study of maternal and neonatal morbidity in relation to use of sequential instruments at operative vaginal delivery. Eur J Obstet Gynecol Reprod Biol 2011;156:41–5. 11. Maharaj D. Assessing cephalopelvic disproportion: back to the basics. Obstet Gynecol Surv 2010;65:387–95. 12. Lenhard MS, Johnson TR, Weckbach S, et al. Pelvimetry revisited: analyzing cephalopelvic disproportion. Eur J Radiol 2010;74: e107–11.
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13. Spo¨rri S, Thoeny HC, Raio L, et al. MR imaging pelvimetry: a useful adjunct in the treatment of women at risk for dystocia? AJR Am J Roentgenol 2002;179:137–44. 14. Peregrine E, O’Brien P, Jauniaux E. Clinical and ultrasound estimation of birth weight prior to induction of labor at term. Ultrasound Obstet Gynecol 2007;29:304–9. 15. Irion O, Boulvain M. Induction of labour for suspected fetal macrosomia. Cochrane Database Syst Rev 2002;(2):CD000938. 16. Ramphul M, Murphy DJ. The role of ultrasound on the labour ward. Expert Rev Obstet Gynecol 2012;7:615–25. 17. Kennelly MM, Anjum R, Lyons S, Burke G. Postpartum fetal head circumference and its influence on labour duration in nullipara. J Obstet Gynaecol 2003;23:496–9. 18. Ayinde OA, Omigbodun AO. Head circumference at time of birth: a possible predictor of labour outcome in singleton cephalic deliveries at term? Ann Afr Med 2004;3:126–9. 19. Elvander C, Ho¨gberg U, Eke´us C. The influence of fetal head circumference on labor outcome: a population-based register study. Acta Obstet Gynecol Scand 2012;91:470–5. 20. Mujugira A, Osoti A, Deya R, et al. Fteal head circumference, operative delivery, and fetal outcomes: a multi-ethnic populationbased cohort study. BMC Preg Childbirth 2013;13:106. 21. Akmal S, Tsoi E, Kametas N, et al. Intrapartum sonography to determine fetal head position. J Matern Fetal Neonatal Med 2002; 12:172–7. 22. Ramphul M, Murphy DJ. Establishing the accuracy and acceptability of abdominal ultrasound to define the fetal head position in the second stage of labour: a validation study. Eur J Obstet Gynecol Reprod Biol 2012;164:35–9. 23. Ramphul M, Ooi PV, Burke G, Instrumental Delivery & UltraSound. A multi-centre randomised controlled trial of ultrasound assessment of the fetal head position versus standard care as an approach to prevent morbidity at instrumental delivery. BJOG 2014;121:1029–38. 24. Snijders RJ, Nicolaides KH. Fetal biometry at 14–40 weeks’ gestation. Ultrasound Obstet Gynecol 1994;4:34–48. 25. Verburg BO, Steegers EA, De Ridder M, et al. New charts for ultrasound dating of pregnancy and assessment of fetal growth: longitudinal data from a population-based cohort study. Ultrasound Obstet Gynecol 2008;31:388–96. 26. Wright CM, Williams AF, Elliman D, et al. Using the New UKWHO growth charts. BMJ 2010;340:c1140. 27. Bahl R, Strachan B, Murphy DJ. Outcome of subsequent pregnancy three years after previous operative delivery in the second stage of labour – cohort study. BMJ 2004;328:311–14.
ISSN: 1476-7058 (Print) 1476-4954 (Online) Journal homepage: http://www.tandfonline.com/loi/ijmf20
Ultrasound assessment of fetal head circumference at the onset of labor as a predictor of operative delivery Poh Vei Ooi, Meenakshi Ramphul, Soha Said, Gerard Burke, Mairead M. Kennelly & Deirdre J. Murphy To cite this article: Poh Vei Ooi, Meenakshi Ramphul, Soha Said, Gerard Burke, Mairead M. Kennelly & Deirdre J. Murphy (2015) Ultrasound assessment of fetal head circumference at the onset of labor as a predictor of operative delivery, The Journal of Maternal-Fetal & Neonatal Medicine, 28:18, 2182-2186, DOI: 10.3109/14767058.2014.980810 To link to this article: http://dx.doi.org/10.3109/14767058.2014.980810
Accepted author version posted online: 03 Nov 2014. Published online: 14 Nov 2014. Submit your article to this journal
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Date: 06 November 2015, At: 05:04
http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, 2015; 28(18): 2182–2186 ! 2014 Informa UK Ltd. DOI: 10.3109/14767058.2014.980810
ORIGINAL ARTICLE
Ultrasound assessment of fetal head circumference at the onset of labor as a predictor of operative delivery Poh Vei Ooi1,2, Meenakshi Ramphul2,3, Soha Said1,4, Gerard Burke1,4, Mairead M. Kennelly2, and Deirdre J. Murphy2,3 University Maternity Hospital, Limerick, Republic of Ireland, 2Department of Obstetrics and Gynaecology, Trinity College, Dublin, Republic of Ireland, 3Coombe Women and Infants University Hospital, Dublin, Republic of Ireland, and 4Department of Obstetrics and Gynaecology, Graduate Entry Medical School, University of Limerick, Limerick, Republic of Ireland
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1
Abstract
Keywords
Objective: This study sought to determine whether ultrasound assessment of fetal head circumference (FHC) at the onset of labor can predict the likelihood of operative delivery. Methods: We performed a prospective cohort study of 200 nulliparous women with singleton, cephalic, term pregnancies in an Irish Maternity Hospital. Transabdominal ultrasound assessment of FHC was performed when spontaneous labor was diagnosed or immediately prior to induction. Odds ratios for operative delivery (instrumental delivery or cesarean section) and maternal and neonatal morbidity were calculated using logistic regression with FHC categorized at a 350-mm cut-off (90th percentile). Results: Ultrasound assessment of FHC at the onset of labor was highly correlated with postdelivery neonatal head circumference (NHC) (Pearson’s correlation coefficient 0.74), suggesting that it can be measured reliably. FHC 350 mm was associated with more than twice the risk of any operative delivery (OR 2.5, 95% CI 1.0–6.2) and a two-fold increased risk of cesarean section for dystocia (OR 2.0, 95% CI 1.0–4.3). Differences in maternal and neonatal morbidity were not statistically significant. Conclusion: These preliminary data suggest that ultrasound assessment of FHC at the onset of labor may be useful in identifying women at greater risk of intrapartum intervention and warrant further research.
Cesarean section, fetal head circumference, instrumental delivery, labor, ultrasound.
Introduction Every year, more than 10 000 women in Ireland give birth by instrumental delivery [1]. Indications for forceps and vacuum include prolonged second stage of labor, suspected fetal compromise and medical disorders that warrant shortening of the active second stage [2–4]. In cases where cephalopelvic disproportion is suspected or instrumental delivery fails, cesarean section plays an essential role [5]. Operative deliveries in the second stage of labor (both instrumental delivery and cesarean section) are associated with significant maternal and perinatal morbidity and mortality, and also with psychological morbidity [5–7]. Forceps delivery and vacuum extraction are associated with maternal urinary dysfunction and perineal trauma including anal sphincter injuries, while perinatal trauma includes scalp laceration, cephalhematoma, retinal hemorrhage, facial nerve and cranial injuries [6–8]. Address for correspondence: Professor Deirdre J. Murphy, Academic Department of Obstetrics & Gynaecology, Trinity College, University of Dublin, Dublin, Republic of Ireland & Coombe Women & Infants University Hospital, Cork Street, Dublin 8, Republic of Ireland. Tel: +353-1-4085200. Direct: +353-1-4082126. Fax: +353-1-4531614. E-mail: [email protected]
History Received 11 August 2014 Revised 19 October 2014 Accepted 22 October 2014 Published online 14 November 2014
Morbidity increases when multiple instruments are used [9,10]. Cesarean section at full dilatation is associated with major maternal hemorrhage, prolonged hospital stay and an increase in neonatal admissions to the intensive care unit [5,7]. Attempts to identify women at highest risk of cephalopelvic disproportion have concluded that neither X-ray, computed tomography or magnetic resonance imaging pelvimetry have a proven value in labor management or clinical outcomes [11–13]. Research evaluating fetal factors in operative delivery has focused mainly on estimated fetal weight to predict macrosomia. However, ultrasound estimation of fetal weight has been shown to differ from actual birth weight by as much as 20%, and identifying suspected fetal macrosomia, other than for diabetic pregnancies, has not been shown to improve labor outcomes [14–15]. A further challenge relates to the timing of ultrasound assessment as several weeks may elapse between the time of antenatal assessment and the onset of labor. The role of ultrasound in labor warrants consideration [16]. Several studies have reported an association between increased neonatal head circumference (NHC) and prolonged second stage of labor, instrumental delivery and cesarean section [17–20]. However, NHC can only be obtained
Ultrasound assessment of FHC
DOI: 10.3109/14767058.2014.980810
following delivery and has no predictive value for interventions in labor. Ultrasound assessment of the fetal head position immediately prior to instrumental delivery has been shown to be feasible and to markedly reduce the incidence of incorrect diagnosis of the fetal head position [21–23]. Fetal head circumference (FHC) is a parameter that is familiar to most novice sonographers and would be relatively simple and attainable in a labor room setting. This study set out to investigate whether ultrasound assessment of the FHC at the onset of labor can be reliably ascertained compared to NHC, and whether it could potentially have a predictive role in identifying women at increased risk of operative delivery by forceps, vacuum or cesarean section.
Methods
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Validation study Prior to commencing the prospective cohort study, a validation study was performed aiming to ascertain the validity and reliability of ultrasound assessment of fetal head measurements as recorded by a novice research sonographer in comparison with an expert sonographer. A total of 35 participants consented to an intrapartum ultrasound scan. All participants were at least 37 weeks gestation and 80% were in the active first stage of labor. Three scan images were taken for each participant, and the results were averaged. Optimal ultrasound measurements of FHC and biparietal diameter (BPD) were obtained in 28 participants (80%), and the remainder was sub-optimal. We considered the FHC and BPD to be optimal when a clear outline of the entire fetal skull was obtained, and the landmarks (the cavum septum pellucidum, thallamus and choroid plexus in the atrium of the lateral ventricles) were visualized. Transabdominal measurements of the FHC were measured by the novice sonographer and the expert, who is a sub-specialist in fetal and maternal medicine, not more than 10 min apart, recorded separately and later analyzed using intraclass correlation coefficients. Bland–Altman plots were constructed to assess level of agreement between novice and expert measurements. A very high correlation between ultrasound measurements of the FHC performed by the novice and expert was demonstrated with a significant intra-class correlation coefficient (ICC) of 0.78, supporting the validity of novice sonographic measurements (inter-observer reliability). High intra-observer reliability was also shown, suggesting good reproducibility not only for expert, but also for novice FHC measurements (ICC 0.88 and 0.83, respectively). Prospective cohort study A prospective cohort study was followed, which was carried out between September 2011 and June 2012 in a regional maternity hospital with over 5000 deliveries annually. Participants included were nulliparous women at term, defined as at least 37 weeks gestation, with singleton cephalic pregnancies aiming to deliver vaginally. Women excluded were those less than 18 years old, who had limited command of the English language, deemed incapable of providing informed consent by the midwife in charge of her care, who had inadequate pain relief or who had systemic opiates in the
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previous 4 h. Potential participants admitted for induction of labor or with a spontaneous onset of labor were approached, and written informed consent was sought if they satisfied the inclusion criteria. We confined the study to nulliparous women in order to increase the probability of operative delivery and therefore the power of the study to detect a statistical difference. Many of the women approached were booked for induction of labor in keeping with the criteria imposed by the research ethics committee in terms of allowing women an appropriate time interval to consider study participation. Participants received a transabdominal ultrasound scan measuring FHC (FHC) at the onset of induced and spontaneous labors, performed by a single research sonographer (as described above). The FHC images were categorized as optimal, satisfactory, poor or unattainable. Subsequent details of labor outcome as well as NHC post-delivery were obtained from maternal and neonatal medical records and recorded in a case report form. The primary outcome of interest was a combined category termed operative delivery that included all instrumental deliveries or cesarean sections. Secondary outcomes included prolonged first and second stage of labor, sequential use of instruments, indication for cesarean section, obstetric anal sphincter injury, primary postpartum hemorrhage (PPH), neonatal trauma and admission to the neonatal unit. The analyses were performed using the Predictive Analytics Software Statistics (PASW version 17). Descriptive statistics were used to characterize the patient population. Primary analyses evaluated the relationship between FHC and operative delivery according to a pre-specified cut-off threshold set at 350 mm based on the 90th percentile for FHC at 38–39 weeks’ gestation on standard fetal growth charts [24,25]. The cut-off for NHC was determined to be 370 mm based on the 90th percentile for UK-WHO growth charts [26]. It is important to note that the FHC is based on an ellipse drawn around the bony skull of the fetal head, and the NHC is a measurement that includes the scalp and subcutaneous tissues and soft tissue swelling as the measurements are taken shortly following birth, hence the difference in the absolute values. These cut-off values were consistent with the 90th percentile for retrospective data obtained by our research group [17]. Results are presented as proportions, odds ratio and 95% confidence intervals, with a two-tailed level of significance (p50.05) ascertained using chi-squared analysis. Secondary analyses of maternal and neonatal morbidity outcomes were performed in the same way. The relationship between individual FHC and the corresponding NHC was analyzed using Pearson’s correlation coefficient with significance calculated using the student’s t test. A receiver operating characteristic (ROC) curve was produced to assess the predictive probability of FHC as a measure for operative delivery (combined instrumental delivery and cesarean section). The area under the curve (AUC) was calculated with 95% confidence intervals.
Results A total of 200 women consented to participate in the study out of 210 eligible women approached. Demographic and obstetric characteristics of the cohort are presented in Table 1,
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Table 1. Characteristics of study population and descriptive statistics for fetal head circumference, biparietal diameter and neonatal head circumference. Characteristics
Mean
N ¼ 200 Maternal age (years) Maternal BMI (kg/m2) Gestational age at delivery (weeks) Cervical dilatation at scan (cm) Birth weight (g) FHC (mm) BPD (mm) NHC (mm)
SD
Median
Min
Max
28.2 25.3 40.0
5.7 5.1 1.1
28.0 24.0 39.9
18.0 16.0 37.3
41.0 40.0 41.7
2.7
1.7
2.0
1.0
10.0
3551.8 339.0 94.1 353.6
451.7 12.7 4.3 14.4
3625.0 340.0 94.0 355.0
2230.0 307.0 77.0 320.0
4750.0 373.0 103.0 390.0
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SD: standard deviation; BMI: body mass index; HC: head circumference; BPD: biparietal diameter; FHC: fetal head circumference; NHC: neonatal head circumference
Table 2. Overall and image-quality adjusted correlation between fetal head circumference and neonatal head circumference.
Characteristics
Mean
Overall (n ¼ 200) Fetal HC 339.0 Neonatal HC 353.6 High quality (n ¼ 170) Fetal HC 339.8 Neonatal HC 353.6
SD
Standard error mean
12.7 14.4 12.4 14.4
Pearson’s correlation
p
0.9 1.0
0.735
0.0001
1.0 1.0
0.813
0.0001
SD: standard deviation; HC: head circumference. High quality: Optimal or satisfactory images obtained.
along with the descriptive statistics for sonographic FHC, BPD and NHC measured post-delivery. All patients were nulliparous, in the first stage of labor and 77% had labor induced. All transabdominal ultrasound assessments were performed within 24 h of delivery. The FHC images were optimal or satisfactory in 170 cases. Spontaneous vaginal delivery occurred in 28% of women, while rates of instrumental delivery and cesarean section were 39 and 34%, respectively. Of the women who had an instrumental delivery, six (3%) involved the use of sequential instruments. For the majority of cases, the instrument used was a disposable vacuum (60%), followed by a metal cup vacuum (23%) and non-rotational forceps (17%). There was a high correlation between sonographic FHC and NHC post-delivery (Pearson’s 0.74, p50.01). Table 2 reports a comparison of the degree of correlation before and after adjusting for image quality, where only high-quality images (optimal or satisfactory) were included (Pearson’s correlation 0.81, p50.01). A ROC curve was produced which demonstrated a significant predictive probability of FHC as a measure for operative delivery; area under curve 0.64 (95% CI 0.54–0.73). Table 3 reports a comparison of labor outcomes between groups for both sonographic FHC and NHC post-delivery. FHC at or above 350 mm was associated with an increased risk of operative delivery (combined instrumental delivery and cesarean section) (OR 2.5, CI 1.04–6.2, p ¼ 0.04).
The risk of cesarean section for dystocia was increased twofold (OR 2.0, CI 1.0–4.2, p ¼ 0.08). NHC at or above 370 mm was associated with an increased risk of instrumental delivery (OR 2.2 CI 1.1–4.5, p ¼ 0.03), but the association with combined operative delivery did not reach statistical significance.
Discussion FHC at the onset of labor was found to be a reliable measure demonstrating high correlation with NHC. NHC has been associated with an increased risk of operative delivery, and similarly, we established that a FHC threshold of 350 mm was associated with a two-fold increased risk of combined operative delivery. The AUC calculated from the ROC graph showed that the predictive potential of FHC as a screening tool for operative delivery in labor is promising and warrants further research. The initial validation study confirmed the accuracy of ultrasound measurements of FHC performed by a novice sonographer compared to an expert and verified the reproducibility of these measures. All of the ultrasound measurements in the prospective cohort study were performed by the same operator, thus ensuring methodological consistency. A deeply engaged fetal head was found in 14% of participants, contributing to difficulties in achieving the precise plane for sonographic FHC measurement, and these images were considered sub-optimal. Even so, analyses with and without sub-optimal images yielded very similar results. Random error was minimized by obtaining and averaging several measurements for each participant in keeping with standard practice for routine antenatal ultrasonography. Further subclassification of labor outcome into sequential instrumental delivery, failed instrumental delivery and obstetric anal sphincter injury resulted in small subgroups thereby limiting statistical analysis. We selected a higher risk population of nulliparous women, many of whom were induced and, while this increased statistical power, the results would not be generalisable to parous women with previous vaginal deliveries. This work should be viewed as preliminary and warrants replication in other settings and populations. A much larger sample size would be required to allow for testing of multiple associations. Comparison with existing literature Several studies have investigated the relationship between ‘‘fetal’’ head circumference and labor outcomes but, in fact, rely on newborn head circumference as a proxy for true FHC. A retrospective study analyzing singleton nulliparous cephalic pregnancies reported that an increased mean duration of labor and a longer second stage of labor were significantly associated with NHC of 370 mm and above [17]. Elvander et al. reported that data from singleton nulliparous deliveries over a 10-year period showing evidence that increasing NHC conferred significantly higher odds for instrumental deliveries as well as cesarean sections [19]. Mujugira et al. had similar findings in a multi-ethnic population [20]. Ayinde et al. examined singleton cephalic nulliparous and multiparous pregnancies and found that the cesarean delivery rate was
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Table 3. Labor outcome according to fetal and neonatal head circumference. Fetal HC* (mm)
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Characteristics 1st Stage 410 hrs 2nd Stage 42 hrs Total labor 412 hrs Operative delivery Total instrumental delivery Single instrument Sequential instruments Total cesarean section Dystocia Fetal distress Failed instrumental Postnatal maternal complication (all) 1 PPH Neonatal trauma Admission to SCBU Perineal trauma
5350 n ¼ 128 (%) 32 38 28 85 43 39 4 42 26 16 0 29 10 43 21 68
(25) (30) (23) (66) (34) (31) (3) (33) (20) (13) (0) (23) (8) (34) (16) (53)
350 n ¼ 42 (%) 11 14 9 35 17 15 2 19 14 4 1 14 6 16 8 21
(26) (33) (21) (83) (41) (36) (5) (45) (33) (10) (2) (33) (14) (38) (19) (50)
Neonatal HC (mm) FHC 350 mm OR (95% CI)
p
1.1 1.2 0.9 2.5 1.3 1.3 1.6 1.7 2.0 0.7
(0.5–2.7) (0.6–4.6) (0.4–2.5) (1.0–6.2) (0.7–2.8) (0.7–2.6) (0.3–8.8) (0.8–3.4) (1.0–4.3) (0.2–2.3)
0.65 0.19 0.91 0.04 0.42 0.53 0.62 0.15 0.08 0.61
1.7 1.4 1.2 1.2 0.7
(0.8–3.7) (0.4–5.3) (0.6–2.5) (0.5–3.0) (0.4–1.5)
0.17 0.59 0.60 0.69 0.37
5370 n ¼ 163 (%) 42 53 35 113 57 54 3 56 38 17 1 37 14 56 26 88
(27) (49) (23) (69) (35) (33) (2) (34) (23) (10) (1) (23) (9) (34) (16) (54)
370 n ¼ 37 (%) 11 14 10 31 20 17 3 11 8 3 0 13 6 19 7 22
(31) (52) (28) (84) (54) (46) (8) (30) (22) (8) (0) (53) (16) (51) (19) (59)
NHC 370 mm OR (95% CI)
P
1.2 1.1 1.3 2.3 2.2 1.7 4.7 0.8 0.9 0.8
(0.5–2.6) (0.5–2.6) (0.6–2.9) (0.9–5.8) (1.1–4.5) (0.8–3.5) (0.9–24.3) (0.4–1.8) (0.4–2.1) (0.2–2.7)
0.69 0.76 0.58 0.08 0.03 0.14 0.04 0.64 0.77 0.67
1.9 2.1 2.0 1.2 1.5
(0.9–4.0) (0.7–5.8) (1.0–4.1) (0.5–3.1) (0.7–3.1)
0.12 0.16 0.05 0.66 0.34
*Fetal HC based on 170 cases with optimal or satisfactory images. HC: head circumference; CI: confidence interval; hrs: hours; 1 PPH: primary postpartum hemorrhage; SCBU: special care baby unit; Operative Delivery: total instrumental delivery and caesarean section; Perineal trauma: 2nd + 3rd degree tear.
significantly higher only in nulliparous pregnancies with NHC measuring 370 mm and above [18]. The novel aspect of our study was the finding of an association between antenatally determined FHC and operative delivery, and a particularly strong association with cesarean section for dystocia. The advantage of this approach is that the information can be ascertained reliably at the onset of labor. Unlike studies exploring the association between estimated fetal weight, actual birth weight and delivery outcomes [14], we found a very strong correlation between FHC and NHC performed shortly following delivery. On average FHC measurements were 15 mm less than NHC measurements which is to be expected given that ultrasound measurement of FHC is based on the bony skull, and neonatal measurement is based on the occipitofrontal circumference including the infants scalp and subcutaneous tissues. Mathematically, the 15-mm difference equates to a 2.5-mm thickness of the soft tissues. We could have evaluated each individual FHC measurement by percentile; however, we choose a cut-off approach based on the 90th percentile at full term for two reasons. Firstly, this approach replicated the previous studies on NHC and allowed direct comparisons to be made, and secondly the choice of an easy to recall cut-off would facilitate interpretation and application of scan findings in the pressurized labor room environment. Operative delivery, particularly in the second stage of labor is a disappointing outcome for laboring women, as well as being associated with increased maternal and perinatal morbidity and implications for subsequent deliveries [5,27]. The ability to identify women at higher risk of operative intervention from the time of admission to the labor ward could have important implications for labor management, use of senior support and decisions on how to approach instrumental delivery. The potential downside of admission ultrasound is that it could introduce negativity at an early stage of labor in relation to the woman’s prospect for an uncomplicated spontaneous vaginal delivery. Clearly, intrapartum
ultrasonography should only be used as a guide alongside the analytical skills and experience of the obstetrician and midwife, as absolute reliance on the predictive ability of labor FHC could adversely affect the threshold for potentially unnecessary cesarean sections.
Conclusions FHC correlated closely with NHC and had a moderate predictive value for operative delivery. An FHC at or above 350 mm at the onset of labor was associated with more than twice the combined risk of instrumental delivery or cesarean section. Further large-scale population-based studies are required to validate these findings. An appropriately powered randomized controlled trial would be required to establish whether routine ultrasonographic assessment of FHC at the onset of labor has the potential to reduce adverse delivery outcomes.
Acknowledgements We would like to thank the obstetricians and midwives for their collaboration as well as the women attending the University Maternity Hospital Limerick who participated in the study.
Declaration of interest The authors acknowledge the financial support from the Health Research Board of Ireland and have no conflicts of interest to declare. We have no conflict of interest to declare. GB and DJM had the original idea for the study. DJM obtained funding and supervised the study, analysis of data and helped draft the manuscript. GB, MK and SS were responsible for validation of sonographic parameters. MR was responsible for classification and verification of image quality. PVO collected the data, carried out the analyses and drafted the manuscript. All authors reviewed and revised the
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manuscript. This study received the ethical approval of the ethics committee of the HSE West University Hospitals Group, Limerick.
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