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Risk factors for failed vacuum extraction and associated complications in term newborn infants: a population-based cohort study a
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Mia Ahlberg , Mikael Norman , Anna Hjelmstedt & Cecilia Ekéus a
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Department of Women's and Children's Health, Division of Reproductive Health and
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Department of Clinical Science, Intervention and Technology, Division of Pediatrics, Karolinska Institutet, Stockholm, Sweden Published online: 30 Jul 2015.
To cite this article: Mia Ahlberg, Mikael Norman, Anna Hjelmstedt & Cecilia Ekéus (2015): Risk factors for failed vacuum extraction and associated complications in term newborn infants: a population-based cohort study, The Journal of MaternalFetal & Neonatal Medicine To link to this article: http://dx.doi.org/10.3109/14767058.2015.1057812
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http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, Early Online: 1–6 ! 2015 Informa UK Ltd. DOI: 10.3109/14767058.2015.1057812
ORIGINAL ARTICLE
Risk factors for failed vacuum extraction and associated complications in term newborn infants: a population-based cohort study Mia Ahlberg1, Mikael Norman2, Anna Hjelmstedt1, and Cecilia Eke´us1 Department of Women’s and Children’s Health, Division of Reproductive Health and 2Department of Clinical Science, Intervention and Technology, Division of Pediatrics, Karolinska Institutet, Stockholm, Sweden
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Abstract
Keywords
Objective: The aims of the present study were to investigate risk factors for failed vacuum extraction (VE), and to compare neonatal complications among infants delivered by failed VE with those delivered by successful VE. Methods: Population-based study including all women (and their newborn infants) with singleton pregnancy who gave birth at term by failed VE (n ¼ 4747) or successful VE (n ¼ 83 671) in Sweden between 1999 and 2010. Failed VE was defined as VE followed by an emergency cesarean section (ECS), forceps, or both forceps and ECS. We used logistic regression to examine the association between failed VE in relation to intracranial hemorrhage, subgaleal hemorrhage, Apgar scores 57 at 5 min, and neonatal convulsions. Results: Risk factors for failed VE included occipito posterior position, mid-pelvic fetal station, high birth weight, short maternal stature, epidural analgesia, and induction of labor. Compared with infants born after a successful VE, those delivered by failed VE had a higher risk of subgaleal hemorrhage OR 7.3 CI (5.5–9.7), convulsions OR 1.9 CI (1.4–2.7), and low Apgar OR 2.6 CI (2.3–3.0), but not of ICH. Conclusion: Failed VE is associated with neonatal complications. Fetal head position and station should be carefully assessed prior to the extraction.
Convulsions, epidemiology, failed vacuum extraction, intracranial hemorrhage, low Apgar scores, obstetrics, subgaleal hematoma, vacuum extraction delivery
Introduction Vacuum extraction (VE) is used when shortening of the second stage of labor is necessary due to prolonged second stage of labor, non-reassuring fetal status or if the woman is unable to push effectively. In Sweden, currently VE is used in 14% of nulliparas and 3% of the multiparas. Forceps, the alternative instrument for assisted vaginal delivery, has decreased and at present only used in 0.1% of all deliveries [1]. Although VE is successfully performed in most cases, failure sometimes occurs. Previous studies have shown that difficult VE (including cup dislodgements, more than three tractions or a duration exceeding 15–20 min) are associated with adverse neonatal outcomes [2,3]. Studies on risk factors for failed VE report to some extent different results. Nulliparity, fetal malposition and mid-pelvic fetal station are all common risk factors for failure, while factors such as maternal age, use of regional anesthesia and body mass index (BMI) are uncertain [4–6]. Furthermore, Address for correspondence: Dr Cecilia Eke´us, Department of Women’s and Children’s Health, Division of Reproductive Health, Karolinska Institutet, Stockholm, Sweden. Tel: +46 709 65 42 68. E-mail: [email protected]
History Received 22 April 2015 Revised 11 May 2015 Accepted 31 May 2015 Published online 27 July 2015
evidence on neonatal complications related to failed VE is not consistent. Smaller studies indicate that failed VE is safe for the infant [7–10]. In contrast, two larger studies showed an association between failed VE and neonatal complications in comparison with spontaneous vaginal delivery [11,12]. The results of previous studies on failed vaginal operative delivery are difficult to compare since some focus on forceps as the subsequent instrument after a failed VE, and others ECS. There is to our knowledge no population-based study that has compared failed VE with successful VE and investigated neonatal complications subsequent failed VE. To justify a frequent use of VE and in some cases as a substitute for cesarean section (CS), the risks for neonatal morbidity after VE need to be more thoroughly described. In particular, the risks for uncommon but serious outcomes such as intracranial hemorrhages and convulsions – which have the potential to cause permanent brain injury – need to be addressed. This study addressed three clinical questions: (1) Has the increased frequency of VE-assisted deliveries been followed by an increased rate of failed VE? (2) Can maternal and obstetric risk factors predict failure with VE? (3) Is failed VE associated with increased risk of neonatal complication?
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To answer these questions, we performed a large populationbased registry study using data on all VE deliveries in Sweden from 1999 to 2010.
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Materials and methods This study was based on data from the Swedish Medical Birth Registry (SMBR). The SMBR includes prospectively collected data on 98% of all births in Sweden. Data are recorded in a standardized way from a woman’s first antenatal visit (occurring before gestational week 15 in 95% of all pregnancies) to postnatal care. The study was approved by the Regional Ethics Committee, Dnr: 2008/1322-31. The study population included all women (and their newborn infants) with singleton pregnancy who gave birth at term (gestational age [GA]436 weeks + 6 d) to a live-born infant in cephalic presentation by VE in Sweden between 1999 and 2010 (n ¼ 88 418). Mode of delivery was categorized into successful vaginal VE, or failed VE, including all infants who were delivered with a VE attempt followed by an ECS, the use of forceps, or both the use of forceps and ECS. During the 12-year period, altogether 1 077 532 women gave birth to a live infant in cephalic presentation in gestational week 436 in Sweden. The rate of planned CS conducted before the onset of labor) increased from 4.1% in 1999 to 5.9% in 2010, and the rate of ECS (performed during labor) increased from 6.3% to 7.1% during this period, see Figure 1. Maternal age was categorized into520, 20–24, 25–29, 30– 34, and 434 years. Maternal height was divided into four groups according to Table 1. BMI was categorized according to the World Health Organization’s definitions as underweight (BMI518.5 kg/m2), normal weight (BMI 18.5– 24.9 kg/m2), overweight (BMI 25.0–29.9 kg/m2), and obese (BMI429.9 kg/m2). GA was divided into term (36 + 6–41 + 6 weeks) or post-term (441 + 6 weeks). GA was recorded in complete weeks and was based on ultrasound dating performed at 17–18 weeks of gestation [13]. Data on epidural analgesia (EA) was coded into yes/no. Indications for VE were classified into prolonged labor (ICD 10 O62.0–2, O63.0–9), signs of fetal distress (ICD 10 O68.0–O68.1–9), maternal exhaustion
9.0% 8.0% 7.0% 6.0% 5.0% 4.0% 3.0% 2.0% 1.0% 0.0%
ECS VE Planned CS
Figure 1. Rate of cesarean section (CS) emergency (ECS) and planned as well as vacuum extraction (VE) between 1999 and 2010 among pregnancies with one live-born infant in cephalic presentation in gestational week436 + 6 d.
(ICD 10 O75.0), any combination of these indications, and missing. The obstetric diagnoses in the SMBR are classified according to the International Classification of Diseases (ICD) tenth (1997 and onwards) revisions [14]. Infant birth weight, position, and station of the fetal head were categorized as displayed in Table 1. The following neonatal outcomes were assessed: intracranial laceration and hemorrhage due to birth injury (P10), intracranial non-traumatic hemorrhage of fetus and newborn (P52), convulsions of newborn (P90), and subgaleal hematoma (P12.2). Low Apgar score was defined as an Apgar score 57 at 5 min. We used logistic regression presented as crude and adjusted odds ratios (OR) and 95% confidence intervals (CI) to estimate the association between maternal, pregnancy and labor, characteristics and the risk of failed VE. In the adjusted model, only variables that were significantly associated with the outcome in the unadjusted model were included. In addition, we conducted logistic regression analyses to estimate crude and adjusted OR with 95% CI for the association between failed VE and adverse neonatal outcomes. Successful VE served as the reference group. To adjust for potential confounders, two models were used: in Model 1, we adjusted for anthropometric characteristics, i.e. year of birth, parity, maternal height, gestational week, sex, and infant birth weight. In Model 2, we added adjustments for obstetric factors, i.e. the induction of labor, episiotomy, the position of the fetal head, the station of the fetal head, EA, and indication for operative delivery. Year of birth was entered as a continuous variable in accordance with a linear secular trend; all other variables were entered as categories. Missing data were entered as a separate category in the analyses. All analyses were calculated using SPSS version 22.0 for Windows (SPSS Inc., Chicago, IL).
Results The overall rate of VE increased from 7.3% 1999 to 8.2% 2010, see Figure 1.Of the total number of 88 418 VEs, 4747 failed. The rate of failed VE increased gradually from 4.9% to 5.4% during the 12-year study period (p ¼ 0.11). Figure 2 shows the rate of different operative methods used after failed VE over the course of the study period. The incidence of failed VE with a subsequent ECS increased during the period, whereas the incidence of failed VE with the subsequent use of forceps decreased. The incidence of a failed VE with the subsequent use of failed forceps and a final ECS remained unchanged at the low level of 0.2%. Table 1 shows the proportion of maternal, pregnancy, delivery, and neonatal characteristics in relation to successful and failed VE, as well as crude and adjusted OR for failed VE. After adjusting for independent risk factors, we found nulliparity, short maternal stature of 5161 cm, and the use of EA to be significantly associated with failed VE. The risk of failed VE also increased with increasing birth weight and increasing GA. Extractions with infants in the occipito posterior position had a six-fold increased risk of failure compared with extractions with infants in the occipito anterior position. VE on stations above the outlet
Vacuum extraction and associated complications in term newborn infants
DOI: 10.3109/14767058.2015.1057812
were associated with a double risk of failure compared with outlet extractions. Episiotomy was performed less often in failed VE compared with successful VE. No differences were found in the risk of failure between the two most
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common indications for VE – prolonged labor and fetal distress. Table 2 shows the crude rates of neonatal complications by mode of delivery. Compared with successful VE, the rates of
Table 1. Proportions of and odds ratios for failed vacuum extraction at term in relation to maternal, pregnancy, labor and neonatal characteristics. Successful VE N ¼ 83 671
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Total ¼ 88 418 Parity Nullipara Multipara Maternal age (y) 520 20–24 25–29 30–34 434 Missing Maternal height (cm) 5155 156–160 161–170 4170 Missing Maternal BMI Underweight Normal Overweight Obese Missing Epidural analgesia No Yes Induction of labor No Yes Indication for operative delivery Prolonged labor Signs of fetal distress Maternal indication Any double indication Missing Fetal position Occiput anterior Occiput posterior Other Fetal station Outlet Above outlet Missing Episiotomy No Yes Gestational age 36 + 6–41 + 6 441 + 6 Infant birth weight (g) 53000 3000–3500 3501–4000 4001–4500 44500 Missing Sex Male Female
Failed VE N ¼ 4747
n
%
n
%
Crude OR CI (95%)
Adjusted OR CI (95%)
66 154 17 517
79.1 20.9
3985 762
83.9 16.1
1.39 (1.28–1.50) 1.0
1.87 (1.70–2.05) 1.0
1339 11 343 27 400 29 094 14 204 291
1.6 13.6 32.7 34.8 17.0 0.3
72 623 1599 1634 805 14
1.5 13.1 33.7 34.4 17.0 0.3
0.9 (0.7–1.17) 0.9 (0.8–1.0) 1.0 1.96 (0.90–1.03) 0.97 (0.89–1.06) 0.82 (0.48–1.41)
3855 12 656 44 407 17 596 5157
4.6 15.1 53.1 21.0 6.2
290 829 2453 904 271
6.1 17.5 51.7 19.0 5.7
1.36 1.19 1.0 0.93 0.95
(1.20–1.55) (1.09–1.29)
1341 31 969 11 822 4146 34 393
1.6 38.2 14.1 5.0 41.1
47 1656 709 290 2045
1.0 34.9 14.9 6.1 43.1
0.68 1.0 1.16 1.35 1.15
(0.50–0.91)
35 140 48 531
42.0 58.0
1572 3175
33.1 66.9
1.0 1.46 (1.38–1.56)
1.0 1.43 (1.33–1.54)
70 596 13 075
84.4 15.6
3838 909
80.9 19.1
1.0 1.28 (1.19–1.38)
1.0 1.14 (1.04–1.25)
26 934 28 707 7058 14 464 6508
32.2 34.3 8.4 17.3 7.8
1881 1277 129 975 485
39.6 26.9 2.7 20.5 10.2
1.0 0.64 0.26 0.97 1.07
1.0 1.06 0.31 1.15 0.98
73 696 7060 2915
88.1 8.4 3.5
2601 1197 949
54.8 25.2 20.0
1.0 4.80 (4.47–5.17) 9.22 (8.49–10.02)
38 192 29 707 15 772
45.6 35.5 18.9
314 597 3836
6.6 12.6 80.8
1.0 2.44 (2.13–2.81) 29.6 (26.3–33.2)
1.0 2.03 (1.77–2.33) 26.8 (23.8–30.1)
59 501 24 170
71.1 28.9
3850 897
81.1 18.9
1.0 0.57 (0.53–0.62)
1.0 0.57 (0.52–0.63)
73 128 10 543
87.4 12.6
3925 822
82.7 17.3
1.0 1.45 (1.34–1.57)
1.0 1.20 (1.09–1.32)
7828 26 156 31 502 14 720 3265 200
9.4 31.3 37.6 17.6 3.9 0.2
259 1102 1879 1125 363 19
5.5 23.2 39.6 23.7 7.6 0.4
0.79 1.0 1.42 1.81 2.64 2.26
0.79 1.0 1.43 1.91 2.92 0.93
47 858 35 809
57.2 42.8
2913 1834
61.4 38.6
1.19 (1.12–1.26) 1.0
BMI, body mass index; CI, confidence intervals; OR, odds ratio; VE, vacuum extraction.
(0.86–1.01) (0.84–1.08)
(1.06–1.27) (1.19–1.54) (1.07–1.23)
( 0.59–0.69) (0.22–0.31) (0.89–1.05) (0.96–1.18)
(0.68–0.90) (1.31–1.53) (1.67–1.98) (2.33–2.99) (1.40–3.62)
1.77 1.32 1.0 0.77 1.01
(1.52–2.05) (1.20–1.45)
0.86 1.0 1.04 1.13 1.01
(0.62–1.19)
(0.71–0.85) (0.87–1.18)
(0.94–1.15) (0.97–1.31) (0.93–1.09)
(0.98–1.16) (0.25–0.37) (1.05–1.26) (0.87–1.10)
1.0 5.95 (5.46–6.48) 7.46 (6.75–8.25)
(0.68–0.93) (1.31–1.56) (1.73–2.12) (2.50–3.40) (0.52–1.64)
1.13 (1.05–1.21) 1.0
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neonatal complications were higher in all kinds of failed VE, regardless of subsequent operative method. Among all VEassisted deliveries, successful and failed, 143 infants were diagnosed with ICH, corresponding to a rate of 1.62/1000. The rate was higher in failed VE: 2.01 in VE+ECS and 1.87 in VE + forceps, respectively, as compared with 1.58 among infants born after a successful VE. Among the 194 infants in which all three methods were used, two infants developed ICH during the 12-year period studied. The highest rates of all the neonatal complications were found in failed extractions followed by a subsequent failed attempt at using forceps and a final ECS. Table 3 shows crude and adjusted logistic regression analysis for the neonatal complications in failed VE with infants born by successful VE as the reference group. After adjustments for anthropometric characteristics (model 1) and obstetric factors (model 2) infants born after failed VE had a significant higher ORs: 7.3, for subgaleal hematoma, 2.6 for low Apgar scores, and 1.9 for convulsions than infants born after successful VE. No statistically significant association between failed VE and ICH was found.
12-years study period and that convulsions, subgaleal hematoma, and low Apgar score, were significantly overrepresented in infants born after failed VE compared with those born after successful VE, also after adjusting for VE-indication. No significant difference in the risk of ICH was found between successful and failed VE. Furthermore, the most pronounced risk factors for failed VE were fetal malposition, extractions conducted from mid-station and high infant birthweight. Compared with occipito anterior position, extractions on occciput posterior- or unknown position was associated with a six to seven time higher risk of failure. The higher rate of failure in malposition is consisted with those of other studies [4,6]. Notably, our results revealed that data on fetal position and fetal station were missing in 20% and 80%, respectively, of all failed extractions. This could reflect that infants in the missing category might have had significantly molding that made the determination of the position difficult, or that the obstetrician, in the cases of a subsequent CS, did not find it important to note the fetal position after the birth. Previous studies have shown that fetal station and position are difficult to evaluate and that vaginal clinical examination of the fetal position are incorrect in 25–50% compared with ultrasound assessments [15,16]. Our results highlight that if position and station are difficult to assess an ultrasonography examination could be used prior the VE. A correct assessment of the fetal position could guide the operator to place the cup correctly over flexion point, choose the appropriate cup and use the right traction angle during VE, in order to minimizing the risk of failure. Most of the other risk factors for failed VE identified in this study, such as high infant birth weight, nulliparity, no episiotomy and induction of labor, are in line with those of previous studies [4–6]. In contrast to the study conducted by Gopalani et al., we could not find any associations between failure and maternal age, BMI, or prolonged labor [5]. Instead, we found that maternal short stature5161 cm was associated with failed VE. Short maternal stature has also been related to increased risk of ICH in infants delivered by VE [17]. EA has previously been reported to be a protective factor for failed instrumental vaginal delivery [6], but inconsistently we found that EA was more commonly used in women with failed VE. Since use of EA is positively correlated with increasing infant birth weight and prolonged labor, it is likely
Discussion The main findings of this population-based study were that the rate of failed VE only increased slightly during the 6.0% 5.0% 4.0% VE+ ECS 3.0%
VE+Forceps VE+Forceps+ECS
2.0% 1.0% 0.0%
Figure 2. Incidence of failed vacuum extractions over the study period 1999–2010.
Table 2. Rate of neonatal morbidity associated with successful or failed VE. Failed VE N ¼ 4747 All
N ¼ 88 418 Intracranial hemorrhage Convulsions Apgar score 57 at 5 min Subgaleal hematoma
Successful VE
VE+ECS
VE + Forceps
VE + Forceps + ECS
N ¼ 83 671
N ¼ 3484
N ¼ 1069
N ¼ 194
N
n
1/1000
n
1/1000
n
1/1000
n
1/1000
143 465 2764 378
132 416 2401 276
1.58 5.0 28.7 3.3
7 36 282 72
2.01 10.3 80.9 20.7
2 10 58 20
1.87 9.4 54.3 18.7
2 3 23 10
10.3 15.5 118.6 51.2
ECS, emergency cesarean section; VE, vacuum extraction.
Vacuum extraction and associated complications in term newborn infants
DOI: 10.3109/14767058.2015.1057812
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Table 3. Logistic regression for successful and failed vacuum extraction and adverse neonatal outcomes. Mode of delivery
Crude OR
(95% CI)
1/1000 Successful VE Failed VE
1.58 2.32
Model 1*
(95 % CI)
Model 2y
(95 % CI)
(0.73,2.50)
1.0 1.33
(0.68,2.62)
(1.42,2.59)
1.0 1.90
(1.36,2.66)
1.0 2.62
(2.30,3.00)
1.0 7.30
(5.51,9.66)
Intracranial hemorrhage 1.0 1.47
(0.79,2.72)
1.0 1.35 Convulsions
Successful VE Failed VE
5.0 10.32
1.0 2.09
(1.55,2.81)
1.0 1.92
Low Apgar scores Successful VE Failed VE
28.7 76.47
1.0 2.80
(2.50,3.14)
1.0 2.65
(2.36,2.97)
Subgaleal hematoma Successful VE Failed VE
3.3 21.49
1.0 6.64
(5.28,8.34)
1.0 6.18
(4.90,7.79)
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VE, vacuum extraction. *Adjusted for year of birth, maternal height, parity, gestational age, sex, birth weight. ySame as in model 1 adding ; episiotomy, induction of labor, EA, fetal station, fetal presentation, indication for operative delivery.
that complications during labor, rather than the EA per se, is related to failed VE. Although regional analgesia might reduce the strengths of contractions during the second stage of labor, the absence of potent analgesia may lead to lack of patient cooperation and difficulties for the women to push because of pain. A recent Swedish study showed that a great proportion of women are delivered by VE without potent pain-relief [18]. We therefore agree with the conclusion of Ben-Haroush and co-authors stating that the use of potent analgesia should be encouraged in women with operative vaginal deliveries. Some studies have reported that failed VE is associated with ICH in newborn infants [11,12]. Although the rate of ICH was higher among infants delivered by failed VE in our study, the association did not reach statistically significance. One likely reason for this non-significantly result is that failed VE, in this study was compared with successful VEs and not with spontaneous vaginal delivery, as in the previous studies. However, in accordance with most other studies [19,20] but not all [21] infants born after a failed VE had a nearly a six-folded risk of subgaleal hemorrhage, a doubled risk of low Apgar score and 60% higher risk for convulsions that those born after a successful VE. Likely explanations are that infants born after a failed VE probably have been exposed to more tractions, cup detachments and longer duration of high pressure against the fetal scalp than infants born after successful VE, and that these factors contributes to these complications [2,3]. In addition, when a subsequent ECS is conducted, the head of the fetus squeezes through the birth canal a second time, which might increase the trauma against the fetal head. We defined failed VE as VE followed by an ECS, the use of forceps, or both the use of forceps and ECS. However, we do not have any information on the exact reason for converting VE to ECS (or forceps). It cannot be excluded that the obstetrician beforehand had decided to perform a VEtrial and to rapidly convert to ECS if the fetus did not follow easily during attempted VE. If such cases existed in our
cohort, they would most likely introduce some conservative bias into our risk estimates of neonatal complications associated with failed VE. In our study, a subsequent ECS was the most common mode of delivery after failed VE. In Sweden, VE has almost replaced the use of forceps, which are currently only used in 0.1% of all births. Hence, it is reasonable to believe that few obstetricians are familiar with using forceps and therefore prefer to conduct an ECS in cases of failed VE. Since we found that neonatal complications were more than doubled among infants delivered with two sequential methods compared with those delivered with merely a subsequent ECS, a subsequent use of forceps should be avoided. This study has several limitations. The register lack detailed information about many factors about VE such as; type of VE instrument used, placement of the cup, number of tractions, traction force, exposure time, strength of contractions, oxytocin use, operators experience or the number of cup detachments. Major strengths include the large study population and the high quality of the registers, making it possible to analyze rare diagnoses and unusual events, such as ICH in infants delivered instrumentally. We were able to include data on risk factors, potential confounders, and outcomes collected independently from one another and without involving the study subjects, thus minimizing various types of bias (e.g. selection and recall bias). Another advantage was the inclusion of the indications for VE, enabling us to address the question of confounding by indication. In summary, infants born after a failed VE are at an increased risk of neonatal complications, especially of subgaleal hematoma. The strongest risk factor for failed VE was an occipito posterior position, mid-pelvic extraction and high infant birth weight. In addition, the increased risk of failed VE in women of short stature should be included in the risk assessment. In the case of a failed VE, a subsequent forceps should not be used.
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Declaration of interest The study was supported by grants from the Swedish Research Council. The authors report no conflict of interests.
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11. 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. 12. Gardella C, Taylor M, Benedetti T, et al. The effect of sequential use of vacuum and forceps for assisted vaginal delivery on neonatal and maternal outcomes. Am J Obstet Gynecol 2001;185:896–902. 13. Høgberg U, Larsson N. Early dating by ultrasound and perinatal outcome. A cohort study. Acta Obstet Gynecol Scand 1997;76: 907–12. 14. Socialstyrelsen: National Board of Health and Welfare, 1996. Swedish Version of International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10). 15. Malvasi A, Tinelli A, Barbera A, et al. Occiput posterior position diagnosis:vaginal examination or intrapartum sonography? A clinical review. J Matern Fetal Neonatal Med 2014;27:520–6. 16. Dupuis O, Ruimark S, Corinne D, et al. Fetal head position during the second stage of labor: comparison of digital vaginal examination and transabdominal ultrasonographic examination. Eur J Obstet Gynecol Reprod Biol 2005;123:193–7. 17. Eke´us C, Ho¨gberg U, Norman M. Vacuum assisted birth and risk for cerebral complications in term newborn infants: a population-based cohort study. BMC Pregn Childbirth 2014;14: 36. 18. Ahlberg M, Saltvedt S, Ekeus C. Insufficient pain relief in vacuum extraction deliveries: a population-based study. Acta Obstet Gynecol Scand 2013;92:306–11. 19. Baskett TF, Fanning CA, Young DC. A prospective observational study of 1000 vacuum assisted deliveries with the OmniCup device. J Obstet Gynaecol Can 2008;30:573–80. 20. Demissie K, Rhoads GG, Smulian JC, et al. Operative vaginal delivery and neonatal and infant adverse outcomes: population based retrospective analysis. BMJ 2004;3;329:24–9. 21. Alexander JM, Leveno KJ, Hauth JC, et al. Failed operative vaginal delivery. Obstet Gynecol 2009;114:1017–22.
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Risk factors for failed vacuum extraction and associated complications in term newborn infants: a population-based cohort study a
b
a
Mia Ahlberg , Mikael Norman , Anna Hjelmstedt & Cecilia Ekéus a
a
Department of Women's and Children's Health, Division of Reproductive Health and
b
Department of Clinical Science, Intervention and Technology, Division of Pediatrics, Karolinska Institutet, Stockholm, Sweden Published online: 30 Jul 2015.
To cite this article: Mia Ahlberg, Mikael Norman, Anna Hjelmstedt & Cecilia Ekéus (2015): Risk factors for failed vacuum extraction and associated complications in term newborn infants: a population-based cohort study, The Journal of MaternalFetal & Neonatal Medicine To link to this article: http://dx.doi.org/10.3109/14767058.2015.1057812
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http://informahealthcare.com/jmf ISSN: 1476-7058 (print), 1476-4954 (electronic) J Matern Fetal Neonatal Med, Early Online: 1–6 ! 2015 Informa UK Ltd. DOI: 10.3109/14767058.2015.1057812
ORIGINAL ARTICLE
Risk factors for failed vacuum extraction and associated complications in term newborn infants: a population-based cohort study Mia Ahlberg1, Mikael Norman2, Anna Hjelmstedt1, and Cecilia Eke´us1 Department of Women’s and Children’s Health, Division of Reproductive Health and 2Department of Clinical Science, Intervention and Technology, Division of Pediatrics, Karolinska Institutet, Stockholm, Sweden
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Abstract
Keywords
Objective: The aims of the present study were to investigate risk factors for failed vacuum extraction (VE), and to compare neonatal complications among infants delivered by failed VE with those delivered by successful VE. Methods: Population-based study including all women (and their newborn infants) with singleton pregnancy who gave birth at term by failed VE (n ¼ 4747) or successful VE (n ¼ 83 671) in Sweden between 1999 and 2010. Failed VE was defined as VE followed by an emergency cesarean section (ECS), forceps, or both forceps and ECS. We used logistic regression to examine the association between failed VE in relation to intracranial hemorrhage, subgaleal hemorrhage, Apgar scores 57 at 5 min, and neonatal convulsions. Results: Risk factors for failed VE included occipito posterior position, mid-pelvic fetal station, high birth weight, short maternal stature, epidural analgesia, and induction of labor. Compared with infants born after a successful VE, those delivered by failed VE had a higher risk of subgaleal hemorrhage OR 7.3 CI (5.5–9.7), convulsions OR 1.9 CI (1.4–2.7), and low Apgar OR 2.6 CI (2.3–3.0), but not of ICH. Conclusion: Failed VE is associated with neonatal complications. Fetal head position and station should be carefully assessed prior to the extraction.
Convulsions, epidemiology, failed vacuum extraction, intracranial hemorrhage, low Apgar scores, obstetrics, subgaleal hematoma, vacuum extraction delivery
Introduction Vacuum extraction (VE) is used when shortening of the second stage of labor is necessary due to prolonged second stage of labor, non-reassuring fetal status or if the woman is unable to push effectively. In Sweden, currently VE is used in 14% of nulliparas and 3% of the multiparas. Forceps, the alternative instrument for assisted vaginal delivery, has decreased and at present only used in 0.1% of all deliveries [1]. Although VE is successfully performed in most cases, failure sometimes occurs. Previous studies have shown that difficult VE (including cup dislodgements, more than three tractions or a duration exceeding 15–20 min) are associated with adverse neonatal outcomes [2,3]. Studies on risk factors for failed VE report to some extent different results. Nulliparity, fetal malposition and mid-pelvic fetal station are all common risk factors for failure, while factors such as maternal age, use of regional anesthesia and body mass index (BMI) are uncertain [4–6]. Furthermore, Address for correspondence: Dr Cecilia Eke´us, Department of Women’s and Children’s Health, Division of Reproductive Health, Karolinska Institutet, Stockholm, Sweden. Tel: +46 709 65 42 68. E-mail: [email protected]
History Received 22 April 2015 Revised 11 May 2015 Accepted 31 May 2015 Published online 27 July 2015
evidence on neonatal complications related to failed VE is not consistent. Smaller studies indicate that failed VE is safe for the infant [7–10]. In contrast, two larger studies showed an association between failed VE and neonatal complications in comparison with spontaneous vaginal delivery [11,12]. The results of previous studies on failed vaginal operative delivery are difficult to compare since some focus on forceps as the subsequent instrument after a failed VE, and others ECS. There is to our knowledge no population-based study that has compared failed VE with successful VE and investigated neonatal complications subsequent failed VE. To justify a frequent use of VE and in some cases as a substitute for cesarean section (CS), the risks for neonatal morbidity after VE need to be more thoroughly described. In particular, the risks for uncommon but serious outcomes such as intracranial hemorrhages and convulsions – which have the potential to cause permanent brain injury – need to be addressed. This study addressed three clinical questions: (1) Has the increased frequency of VE-assisted deliveries been followed by an increased rate of failed VE? (2) Can maternal and obstetric risk factors predict failure with VE? (3) Is failed VE associated with increased risk of neonatal complication?
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M. Ahlberg et al.
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To answer these questions, we performed a large populationbased registry study using data on all VE deliveries in Sweden from 1999 to 2010.
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Materials and methods This study was based on data from the Swedish Medical Birth Registry (SMBR). The SMBR includes prospectively collected data on 98% of all births in Sweden. Data are recorded in a standardized way from a woman’s first antenatal visit (occurring before gestational week 15 in 95% of all pregnancies) to postnatal care. The study was approved by the Regional Ethics Committee, Dnr: 2008/1322-31. The study population included all women (and their newborn infants) with singleton pregnancy who gave birth at term (gestational age [GA]436 weeks + 6 d) to a live-born infant in cephalic presentation by VE in Sweden between 1999 and 2010 (n ¼ 88 418). Mode of delivery was categorized into successful vaginal VE, or failed VE, including all infants who were delivered with a VE attempt followed by an ECS, the use of forceps, or both the use of forceps and ECS. During the 12-year period, altogether 1 077 532 women gave birth to a live infant in cephalic presentation in gestational week 436 in Sweden. The rate of planned CS conducted before the onset of labor) increased from 4.1% in 1999 to 5.9% in 2010, and the rate of ECS (performed during labor) increased from 6.3% to 7.1% during this period, see Figure 1. Maternal age was categorized into520, 20–24, 25–29, 30– 34, and 434 years. Maternal height was divided into four groups according to Table 1. BMI was categorized according to the World Health Organization’s definitions as underweight (BMI518.5 kg/m2), normal weight (BMI 18.5– 24.9 kg/m2), overweight (BMI 25.0–29.9 kg/m2), and obese (BMI429.9 kg/m2). GA was divided into term (36 + 6–41 + 6 weeks) or post-term (441 + 6 weeks). GA was recorded in complete weeks and was based on ultrasound dating performed at 17–18 weeks of gestation [13]. Data on epidural analgesia (EA) was coded into yes/no. Indications for VE were classified into prolonged labor (ICD 10 O62.0–2, O63.0–9), signs of fetal distress (ICD 10 O68.0–O68.1–9), maternal exhaustion
9.0% 8.0% 7.0% 6.0% 5.0% 4.0% 3.0% 2.0% 1.0% 0.0%
ECS VE Planned CS
Figure 1. Rate of cesarean section (CS) emergency (ECS) and planned as well as vacuum extraction (VE) between 1999 and 2010 among pregnancies with one live-born infant in cephalic presentation in gestational week436 + 6 d.
(ICD 10 O75.0), any combination of these indications, and missing. The obstetric diagnoses in the SMBR are classified according to the International Classification of Diseases (ICD) tenth (1997 and onwards) revisions [14]. Infant birth weight, position, and station of the fetal head were categorized as displayed in Table 1. The following neonatal outcomes were assessed: intracranial laceration and hemorrhage due to birth injury (P10), intracranial non-traumatic hemorrhage of fetus and newborn (P52), convulsions of newborn (P90), and subgaleal hematoma (P12.2). Low Apgar score was defined as an Apgar score 57 at 5 min. We used logistic regression presented as crude and adjusted odds ratios (OR) and 95% confidence intervals (CI) to estimate the association between maternal, pregnancy and labor, characteristics and the risk of failed VE. In the adjusted model, only variables that were significantly associated with the outcome in the unadjusted model were included. In addition, we conducted logistic regression analyses to estimate crude and adjusted OR with 95% CI for the association between failed VE and adverse neonatal outcomes. Successful VE served as the reference group. To adjust for potential confounders, two models were used: in Model 1, we adjusted for anthropometric characteristics, i.e. year of birth, parity, maternal height, gestational week, sex, and infant birth weight. In Model 2, we added adjustments for obstetric factors, i.e. the induction of labor, episiotomy, the position of the fetal head, the station of the fetal head, EA, and indication for operative delivery. Year of birth was entered as a continuous variable in accordance with a linear secular trend; all other variables were entered as categories. Missing data were entered as a separate category in the analyses. All analyses were calculated using SPSS version 22.0 for Windows (SPSS Inc., Chicago, IL).
Results The overall rate of VE increased from 7.3% 1999 to 8.2% 2010, see Figure 1.Of the total number of 88 418 VEs, 4747 failed. The rate of failed VE increased gradually from 4.9% to 5.4% during the 12-year study period (p ¼ 0.11). Figure 2 shows the rate of different operative methods used after failed VE over the course of the study period. The incidence of failed VE with a subsequent ECS increased during the period, whereas the incidence of failed VE with the subsequent use of forceps decreased. The incidence of a failed VE with the subsequent use of failed forceps and a final ECS remained unchanged at the low level of 0.2%. Table 1 shows the proportion of maternal, pregnancy, delivery, and neonatal characteristics in relation to successful and failed VE, as well as crude and adjusted OR for failed VE. After adjusting for independent risk factors, we found nulliparity, short maternal stature of 5161 cm, and the use of EA to be significantly associated with failed VE. The risk of failed VE also increased with increasing birth weight and increasing GA. Extractions with infants in the occipito posterior position had a six-fold increased risk of failure compared with extractions with infants in the occipito anterior position. VE on stations above the outlet
Vacuum extraction and associated complications in term newborn infants
DOI: 10.3109/14767058.2015.1057812
were associated with a double risk of failure compared with outlet extractions. Episiotomy was performed less often in failed VE compared with successful VE. No differences were found in the risk of failure between the two most
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common indications for VE – prolonged labor and fetal distress. Table 2 shows the crude rates of neonatal complications by mode of delivery. Compared with successful VE, the rates of
Table 1. Proportions of and odds ratios for failed vacuum extraction at term in relation to maternal, pregnancy, labor and neonatal characteristics. Successful VE N ¼ 83 671
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Total ¼ 88 418 Parity Nullipara Multipara Maternal age (y) 520 20–24 25–29 30–34 434 Missing Maternal height (cm) 5155 156–160 161–170 4170 Missing Maternal BMI Underweight Normal Overweight Obese Missing Epidural analgesia No Yes Induction of labor No Yes Indication for operative delivery Prolonged labor Signs of fetal distress Maternal indication Any double indication Missing Fetal position Occiput anterior Occiput posterior Other Fetal station Outlet Above outlet Missing Episiotomy No Yes Gestational age 36 + 6–41 + 6 441 + 6 Infant birth weight (g) 53000 3000–3500 3501–4000 4001–4500 44500 Missing Sex Male Female
Failed VE N ¼ 4747
n
%
n
%
Crude OR CI (95%)
Adjusted OR CI (95%)
66 154 17 517
79.1 20.9
3985 762
83.9 16.1
1.39 (1.28–1.50) 1.0
1.87 (1.70–2.05) 1.0
1339 11 343 27 400 29 094 14 204 291
1.6 13.6 32.7 34.8 17.0 0.3
72 623 1599 1634 805 14
1.5 13.1 33.7 34.4 17.0 0.3
0.9 (0.7–1.17) 0.9 (0.8–1.0) 1.0 1.96 (0.90–1.03) 0.97 (0.89–1.06) 0.82 (0.48–1.41)
3855 12 656 44 407 17 596 5157
4.6 15.1 53.1 21.0 6.2
290 829 2453 904 271
6.1 17.5 51.7 19.0 5.7
1.36 1.19 1.0 0.93 0.95
(1.20–1.55) (1.09–1.29)
1341 31 969 11 822 4146 34 393
1.6 38.2 14.1 5.0 41.1
47 1656 709 290 2045
1.0 34.9 14.9 6.1 43.1
0.68 1.0 1.16 1.35 1.15
(0.50–0.91)
35 140 48 531
42.0 58.0
1572 3175
33.1 66.9
1.0 1.46 (1.38–1.56)
1.0 1.43 (1.33–1.54)
70 596 13 075
84.4 15.6
3838 909
80.9 19.1
1.0 1.28 (1.19–1.38)
1.0 1.14 (1.04–1.25)
26 934 28 707 7058 14 464 6508
32.2 34.3 8.4 17.3 7.8
1881 1277 129 975 485
39.6 26.9 2.7 20.5 10.2
1.0 0.64 0.26 0.97 1.07
1.0 1.06 0.31 1.15 0.98
73 696 7060 2915
88.1 8.4 3.5
2601 1197 949
54.8 25.2 20.0
1.0 4.80 (4.47–5.17) 9.22 (8.49–10.02)
38 192 29 707 15 772
45.6 35.5 18.9
314 597 3836
6.6 12.6 80.8
1.0 2.44 (2.13–2.81) 29.6 (26.3–33.2)
1.0 2.03 (1.77–2.33) 26.8 (23.8–30.1)
59 501 24 170
71.1 28.9
3850 897
81.1 18.9
1.0 0.57 (0.53–0.62)
1.0 0.57 (0.52–0.63)
73 128 10 543
87.4 12.6
3925 822
82.7 17.3
1.0 1.45 (1.34–1.57)
1.0 1.20 (1.09–1.32)
7828 26 156 31 502 14 720 3265 200
9.4 31.3 37.6 17.6 3.9 0.2
259 1102 1879 1125 363 19
5.5 23.2 39.6 23.7 7.6 0.4
0.79 1.0 1.42 1.81 2.64 2.26
0.79 1.0 1.43 1.91 2.92 0.93
47 858 35 809
57.2 42.8
2913 1834
61.4 38.6
1.19 (1.12–1.26) 1.0
BMI, body mass index; CI, confidence intervals; OR, odds ratio; VE, vacuum extraction.
(0.86–1.01) (0.84–1.08)
(1.06–1.27) (1.19–1.54) (1.07–1.23)
( 0.59–0.69) (0.22–0.31) (0.89–1.05) (0.96–1.18)
(0.68–0.90) (1.31–1.53) (1.67–1.98) (2.33–2.99) (1.40–3.62)
1.77 1.32 1.0 0.77 1.01
(1.52–2.05) (1.20–1.45)
0.86 1.0 1.04 1.13 1.01
(0.62–1.19)
(0.71–0.85) (0.87–1.18)
(0.94–1.15) (0.97–1.31) (0.93–1.09)
(0.98–1.16) (0.25–0.37) (1.05–1.26) (0.87–1.10)
1.0 5.95 (5.46–6.48) 7.46 (6.75–8.25)
(0.68–0.93) (1.31–1.56) (1.73–2.12) (2.50–3.40) (0.52–1.64)
1.13 (1.05–1.21) 1.0
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neonatal complications were higher in all kinds of failed VE, regardless of subsequent operative method. Among all VEassisted deliveries, successful and failed, 143 infants were diagnosed with ICH, corresponding to a rate of 1.62/1000. The rate was higher in failed VE: 2.01 in VE+ECS and 1.87 in VE + forceps, respectively, as compared with 1.58 among infants born after a successful VE. Among the 194 infants in which all three methods were used, two infants developed ICH during the 12-year period studied. The highest rates of all the neonatal complications were found in failed extractions followed by a subsequent failed attempt at using forceps and a final ECS. Table 3 shows crude and adjusted logistic regression analysis for the neonatal complications in failed VE with infants born by successful VE as the reference group. After adjustments for anthropometric characteristics (model 1) and obstetric factors (model 2) infants born after failed VE had a significant higher ORs: 7.3, for subgaleal hematoma, 2.6 for low Apgar scores, and 1.9 for convulsions than infants born after successful VE. No statistically significant association between failed VE and ICH was found.
12-years study period and that convulsions, subgaleal hematoma, and low Apgar score, were significantly overrepresented in infants born after failed VE compared with those born after successful VE, also after adjusting for VE-indication. No significant difference in the risk of ICH was found between successful and failed VE. Furthermore, the most pronounced risk factors for failed VE were fetal malposition, extractions conducted from mid-station and high infant birthweight. Compared with occipito anterior position, extractions on occciput posterior- or unknown position was associated with a six to seven time higher risk of failure. The higher rate of failure in malposition is consisted with those of other studies [4,6]. Notably, our results revealed that data on fetal position and fetal station were missing in 20% and 80%, respectively, of all failed extractions. This could reflect that infants in the missing category might have had significantly molding that made the determination of the position difficult, or that the obstetrician, in the cases of a subsequent CS, did not find it important to note the fetal position after the birth. Previous studies have shown that fetal station and position are difficult to evaluate and that vaginal clinical examination of the fetal position are incorrect in 25–50% compared with ultrasound assessments [15,16]. Our results highlight that if position and station are difficult to assess an ultrasonography examination could be used prior the VE. A correct assessment of the fetal position could guide the operator to place the cup correctly over flexion point, choose the appropriate cup and use the right traction angle during VE, in order to minimizing the risk of failure. Most of the other risk factors for failed VE identified in this study, such as high infant birth weight, nulliparity, no episiotomy and induction of labor, are in line with those of previous studies [4–6]. In contrast to the study conducted by Gopalani et al., we could not find any associations between failure and maternal age, BMI, or prolonged labor [5]. Instead, we found that maternal short stature5161 cm was associated with failed VE. Short maternal stature has also been related to increased risk of ICH in infants delivered by VE [17]. EA has previously been reported to be a protective factor for failed instrumental vaginal delivery [6], but inconsistently we found that EA was more commonly used in women with failed VE. Since use of EA is positively correlated with increasing infant birth weight and prolonged labor, it is likely
Discussion The main findings of this population-based study were that the rate of failed VE only increased slightly during the 6.0% 5.0% 4.0% VE+ ECS 3.0%
VE+Forceps VE+Forceps+ECS
2.0% 1.0% 0.0%
Figure 2. Incidence of failed vacuum extractions over the study period 1999–2010.
Table 2. Rate of neonatal morbidity associated with successful or failed VE. Failed VE N ¼ 4747 All
N ¼ 88 418 Intracranial hemorrhage Convulsions Apgar score 57 at 5 min Subgaleal hematoma
Successful VE
VE+ECS
VE + Forceps
VE + Forceps + ECS
N ¼ 83 671
N ¼ 3484
N ¼ 1069
N ¼ 194
N
n
1/1000
n
1/1000
n
1/1000
n
1/1000
143 465 2764 378
132 416 2401 276
1.58 5.0 28.7 3.3
7 36 282 72
2.01 10.3 80.9 20.7
2 10 58 20
1.87 9.4 54.3 18.7
2 3 23 10
10.3 15.5 118.6 51.2
ECS, emergency cesarean section; VE, vacuum extraction.
Vacuum extraction and associated complications in term newborn infants
DOI: 10.3109/14767058.2015.1057812
5
Table 3. Logistic regression for successful and failed vacuum extraction and adverse neonatal outcomes. Mode of delivery
Crude OR
(95% CI)
1/1000 Successful VE Failed VE
1.58 2.32
Model 1*
(95 % CI)
Model 2y
(95 % CI)
(0.73,2.50)
1.0 1.33
(0.68,2.62)
(1.42,2.59)
1.0 1.90
(1.36,2.66)
1.0 2.62
(2.30,3.00)
1.0 7.30
(5.51,9.66)
Intracranial hemorrhage 1.0 1.47
(0.79,2.72)
1.0 1.35 Convulsions
Successful VE Failed VE
5.0 10.32
1.0 2.09
(1.55,2.81)
1.0 1.92
Low Apgar scores Successful VE Failed VE
28.7 76.47
1.0 2.80
(2.50,3.14)
1.0 2.65
(2.36,2.97)
Subgaleal hematoma Successful VE Failed VE
3.3 21.49
1.0 6.64
(5.28,8.34)
1.0 6.18
(4.90,7.79)
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VE, vacuum extraction. *Adjusted for year of birth, maternal height, parity, gestational age, sex, birth weight. ySame as in model 1 adding ; episiotomy, induction of labor, EA, fetal station, fetal presentation, indication for operative delivery.
that complications during labor, rather than the EA per se, is related to failed VE. Although regional analgesia might reduce the strengths of contractions during the second stage of labor, the absence of potent analgesia may lead to lack of patient cooperation and difficulties for the women to push because of pain. A recent Swedish study showed that a great proportion of women are delivered by VE without potent pain-relief [18]. We therefore agree with the conclusion of Ben-Haroush and co-authors stating that the use of potent analgesia should be encouraged in women with operative vaginal deliveries. Some studies have reported that failed VE is associated with ICH in newborn infants [11,12]. Although the rate of ICH was higher among infants delivered by failed VE in our study, the association did not reach statistically significance. One likely reason for this non-significantly result is that failed VE, in this study was compared with successful VEs and not with spontaneous vaginal delivery, as in the previous studies. However, in accordance with most other studies [19,20] but not all [21] infants born after a failed VE had a nearly a six-folded risk of subgaleal hemorrhage, a doubled risk of low Apgar score and 60% higher risk for convulsions that those born after a successful VE. Likely explanations are that infants born after a failed VE probably have been exposed to more tractions, cup detachments and longer duration of high pressure against the fetal scalp than infants born after successful VE, and that these factors contributes to these complications [2,3]. In addition, when a subsequent ECS is conducted, the head of the fetus squeezes through the birth canal a second time, which might increase the trauma against the fetal head. We defined failed VE as VE followed by an ECS, the use of forceps, or both the use of forceps and ECS. However, we do not have any information on the exact reason for converting VE to ECS (or forceps). It cannot be excluded that the obstetrician beforehand had decided to perform a VEtrial and to rapidly convert to ECS if the fetus did not follow easily during attempted VE. If such cases existed in our
cohort, they would most likely introduce some conservative bias into our risk estimates of neonatal complications associated with failed VE. In our study, a subsequent ECS was the most common mode of delivery after failed VE. In Sweden, VE has almost replaced the use of forceps, which are currently only used in 0.1% of all births. Hence, it is reasonable to believe that few obstetricians are familiar with using forceps and therefore prefer to conduct an ECS in cases of failed VE. Since we found that neonatal complications were more than doubled among infants delivered with two sequential methods compared with those delivered with merely a subsequent ECS, a subsequent use of forceps should be avoided. This study has several limitations. The register lack detailed information about many factors about VE such as; type of VE instrument used, placement of the cup, number of tractions, traction force, exposure time, strength of contractions, oxytocin use, operators experience or the number of cup detachments. Major strengths include the large study population and the high quality of the registers, making it possible to analyze rare diagnoses and unusual events, such as ICH in infants delivered instrumentally. We were able to include data on risk factors, potential confounders, and outcomes collected independently from one another and without involving the study subjects, thus minimizing various types of bias (e.g. selection and recall bias). Another advantage was the inclusion of the indications for VE, enabling us to address the question of confounding by indication. In summary, infants born after a failed VE are at an increased risk of neonatal complications, especially of subgaleal hematoma. The strongest risk factor for failed VE was an occipito posterior position, mid-pelvic extraction and high infant birth weight. In addition, the increased risk of failed VE in women of short stature should be included in the risk assessment. In the case of a failed VE, a subsequent forceps should not be used.
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Declaration of interest The study was supported by grants from the Swedish Research Council. The authors report no conflict of interests.
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