Objective
Previous studies of induction of labor in the setting of trial of labor after cesarean have compared women undergoing trial of labor after cesarean to those undergoing spontaneous labor. However, the clinically relevant comparison is to those undergoing expectant management. The objective of this study was to compare obstetric outcomes between women undergoing induction of labor and those undergoing expectant management ≥39 weeks of gestation.
Study Design
This was a secondary analysis of data from the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network Cesarean Registry that included women with singleton gestations at a gestational age of ≥39 weeks and a history of 1 low transverse cesarean delivery. Outcomes of induction at 39, 40, and 41 weeks were compared to expectant management beyond each gestational age period using univariable and multivariable analyses. Women with scheduled repeat cesarean deliveries done for the indication of prior cesarean delivery were excluded from the analysis.
Results
In all, 12,676 women were eligible for analysis. The rate of vaginal birth after cesarean (VBAC) was higher among women undergoing induction of labor at 39 weeks compared to expectant management (73.8% vs 61.3%, P < .001). The risk of uterine rupture also was higher among women undergoing induction of labor at 39 weeks compared to expectant management (1.4% vs 0.5%, P = .006, respectively). In multivariable analysis, induction of labor at 39 weeks remained associated with a significantly higher chance of VBAC and uterine rupture (odds ratio, 1.31; 95% confidence interval, 1.03–1.67; and odds ratio, 2.73; 95% confidence interval, 1.22–6.12, respectively).
Conclusion
Induction of labor at 39 weeks, when compared to expectant management, was associated with a higher chance of VBAC but also of uterine rupture.
It is commonly believed that women with a prior cesarean delivery who undergo induction of labor are less likely to have vaginal birth after cesarean (VBAC). Indeed, observational studies have consistently shown that women who are induced after a prior cesarean have a 15-20% higher chance of cesarean delivery. In addition, several studies have shown that induction of labor is associated with an approximately 2-fold increased risk of uterine rupture.
However, these conclusions are from comparisons with women who were in spontaneous labor. Caughey et al and others have demonstrated how this comparison group is not clinically relevant, because the actual alternative to induction is not spontaneous labor but expectant management. In fact, among women without a prior cesarean delivery, when labor induction has been compared to expectant management instead of spontaneous labor, metaanalysis of observational studies has revealed a lower chance of cesarean delivery among those who were induced.
The consequences of labor induction compared to expectant management among women with a prior cesarean remain uncertain. We hypothesized that induction of labor ≥39 0/7 weeks of gestation would not be associated with an increased chance of cesarean when compared to expectant management among women planning trial of labor after cesarean. We also investigated whether labor induction is associated with an increase in the risk of uterine rupture or other obstetric morbidities.
Materials and Methods
This was a secondary analysis of data from the Cesarean Registry of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. That registry was the result of a 4–year multicenter observational study, designed to address clinical issues related to cesarean childbirth. In the present analysis, we included all women from the registry who had a history of 1 cesarean delivery via a low transverse or unknown uterine incision and were at a gestational age of at least 39 0/7 weeks. Women with scheduled repeat cesarean deliveries done for the indication of prior cesarean delivery were excluded from the analysis.
Women who underwent labor induction were divided into 3 comparison groups based on the timing of their induction of labor: 39 0/7 -39 3/7 , 40 0/7 -40 3/7 , and 41 0/7 -41 3/7 weeks. Gestational age was based on the best obstetric estimate (last menstrual period compared with ultrasonography), determined by health care providers and used for clinical decision-making. Women who underwent induction during each gestational age window were compared with women who were managed expectantly after the same gestational age window. This design was used to mimic the prospective choice of undertaking a labor induction during a given period of time at the start of a given week of gestation or undergoing expectant management from that time forward. In an effort to evaluate women who were not in need of immediate delivery due to the onset of an acute obstetric complication, women were excluded from the induction group when they had an acute obstetric medical indication for induction (ie, preeclampsia, gestational hypertension, nonreassuring antenatal surveillance, oligohydramnios, fetal growth restriction, and antenatal intrauterine fetal demise). However, if women developed these conditions while they were being expectantly managed, they were not excluded from the expectant management group, as 1 consequence of expectant management is that these conditions may develop and require delivery.
A recurrent indication for cesarean delivery was defined as a cesarean due to any type of arrest disorder. Uterine rupture was defined as a disruption or tear of the uterine muscle and visceral peritoneum or a separation of the uterine muscle with extension to the bladder or broad ligament.
To ensure that our results were not solely dependent upon our primary analytic approach and group composition, we performed additional analyses in which the inclusion criteria for the group of women expectantly managed was altered slightly. In 1 analysis, we included women who underwent labor from the first day at which women also may have undergone labor induction (ie, laboring women were included in the expectantly managed group from 39 0/7 weeks, instead of only from 39 4/7 weeks as in the primary analysis). In another analysis, we included women in the expectant management group if they remained pregnant at least 1 week longer than the first day women underwent labor induction in the comparison group but then underwent a scheduled repeat cesarean with prior cesarean as the primary indication, given it is possible that these women initially may have chosen expectant management (instead of planned cesarean) but then decided to forego trial of labor after cesarean when they had not labored by a given gestational age.
All analyses were performed with software (Stata, version 12.0; StataCorp, College Station, TX). Univariable comparisons of maternal and neonatal characteristics and pregnancy outcomes were performed using Pearson χ 2 test and Fisher exact test for categorical data and the Student t test for continuous measures. Additionally, multivariable logistic regression was performed for the outcomes that were significantly different in univariable analysis. Potential confounding variables were entered into the regression equation if they differed between groups in univariable analysis at a level of P < .05. Odds ratios with 95% confidence intervals were estimated from the logistic regression. This study was considered exempt by the Northwestern University Institutional Review Board because only de-identified data were used.
Results
In all, 12,676 women were eligible for analysis. Maternal characteristics of the study population according to the gestational age at which they underwent labor induction or expectant management are depicted in Table 1 . Women undergoing induction of labor differed in several ways from those who were expectantly managed, including in their age, race, and obstetric history.
| Characteristic | IOL | EM | IOL | EM | IOL | EM |
|---|---|---|---|---|---|---|
| 39 0/7 –39 3/7 wk (n = 638) | >39 3/7 wk (n = 7565) | 40 0/7 –40 3/7 wk (n = 522) | >40 3/7 wk (n = 2933) | 41 0/7 –41 3/7 wk (n = 471) | >41 3/7 wk (n = 547) | |
| Age, y | 30.2 ± 5.4 b | 28.1 ± 5.7 | 29.7 ± 5.4 b | 27.7 ± 5.7 | 28.7 ± 5.5 b | 27.4 ± 5.6 |
| Prepregnancy BMI | 27.0 ± 6.6 | 26.7 ± 6.3 | 27.3 ± 6.7 | 27.0 ± 6.4 | 27.6 ± 7.3 | 27.3 ± 6.1 |
| Race | ||||||
| African American | 157 (24.6) b | 2556 (33.8) | 159 (30.4) b | 1066 (36.3) | 157 (33.3) b | 220 (40.2) |
| Caucasian | 391 (61.3) b | 2116 (27.9) | 263 (50.4) b | 733 (25.0) | 188 (39.9) b | 104 (19.0) |
| Hispanic | 55 (8.6) b | 2473 (32.7) | 69 (13.2) b | 973 (33.2) | 94 (20.0) b | 191 (34.9) |
| Other | 35 (5.5) b | 421 (5.6) | 30 (5.7) b | 160 (5.4) | 32 (6.8) b | 32 (5.8) |
| Cigarette use during | 75 (11.7) | 971 (12.8) | 69 (13.2) | 395 (13.5) | 67 (14.2) | 96 (17.6) |
| Pregnancy | ||||||
| Prior vaginal delivery | 362 (56.8) b | 3228 (42.9) | 238 (46.1) | 1270 (43.6) | 188 (39.9) b | 255 (47.0) |
| Prior VBAC | 254 (39.8) b | 2010 (26.5) | 169 (32.4) b | 777 (26.5) | 117 (24.8) | 153 (28.0) |
| Recurrent indication for prior | 173 (27.1) b | 2475 (39.8) | 169 (32.4) | 937 (38.5) | 145 (30.8) | 193 (40.2) |
| CD | ||||||
| Chronic medical illness a | 9 (1.4) | 63 (0.8) | 6 (1.1) | 17 (0.6) | 4 (0.8) | 5 (0.9) |
a Includes chronic hypertension, pregestational diabetes, asthma, seizure disorder, thyroid disease, or renal insufficiency
b P < .05 for comparison of labor induction vs EM at given gestational age.
Maternal outcomes are depicted in Table 2 . Women induced at 39 0/7 -39 3/7 weeks compared to those who were managed expectantly had higher rates of VBAC. A higher chance of VBAC similarly was noted among women who were induced at 40 0/7 -40 3/7 weeks, compared to those expectantly managed beyond that gestational age, but the results did not reach statistical significance. Women induced at 39 0/7 -39 3/7 weeks also had a higher chance of uterine rupture compared to women managed expectantly beyond that gestational age ( Table 2 ). There were no other differences in obstetric morbidity between women who were induced and who were expectantly managed.
| Maternal outcome | IOL | EM | IOL | EM | IOL | EM |
|---|---|---|---|---|---|---|
| 39 0/7 –39 3/7 wk (n = 638) | >39 3/7 wk (n = 7565 ) | 40 0/7 –40 3/7 wk (n = 522) | >40 3/7 wk (n = 2933) | 41 0/7 –41 3/7 wk (n = 471) | >41 3/7 wk (n = 547) | |
| VBAC | 471 (73.8) b | 4640 (61.3) | 340 (65.1) | 1817 (61.9) | 277 (58.8) | 330 (60.3) |
| Third/fourth degree | 28 (4.4) | 311 (4.1) | 30 (5.7) | 108 (3.7) | 27 (5.7) | 14 (2.5) |
| Endometritis | 13 (2.0) | 255 (3.4) | 12 (2.3) | 115 (3.9) | 20 (4.2) | 16 (2.9) |
| Wound complication | 4 (0.6) | 29 (0.4) | 4 (0.7) | 12 (0.4) | 1 (0.2) | 2 (0.3) |
| Blood transfusion | 6 (0.9) | 122 (1.6) | 14 (2.7) | 45 (1.5) | 9 (1.9) | 11 (2.0) |
| Operative complications a | 1 (0.1) | 22 (0.3) | 4 (0.7) | 10 (0.3) | 0 | 1 (0.2) |
| Uterine rupture | 9 (1.4) b | 40 (0.5) | 7 (1.3) | 17 (0.6) | 6 (1.3) | 2 (0.4) |
| Hysterectomy | 0 | 11 (0.1) | 3 (0.6) | 5 (0.2) | 0 | 3 (0.5) |
| ICU admission | 1 (0.1) | 21 (0.3) | 3 (0.6) | 7 (0.2) | 0 | 1 (0.2) |
| Maternal death | 0 | 1 (0.01) | 1 (0.2) | 0 | 0 | 0 |
a Cystotomy, ureteral injury, bowel injury
b P < .05 for comparison of labor induction vs EM at given gestational age.
Neonatal characteristics and outcomes are depicted in Table 3 . Neonates of women who were induced at 39 0/7 -39 3/7 and 40 0/7 -40 3/7 weeks had lower birthweight compared to neonates whose mothers were managed expectantly ( P < .001 and P = .03, respectively). Overall, neonatal outcomes at each gestational age did not differ significantly among the comparison groups. The point estimates of the frequencies of neonatal intensive care unit admission, hypoxic-ischemic encephalopathy, and perinatal death were higher among neonates whose mothers were in the expectant management groups, however these differences did not reach statistical significance ( Table 3 ).
| Variable | IOL | EM | IOL | EM | IOL | EM |
|---|---|---|---|---|---|---|
| 39 0/7 –39 3/7 wk (n = 638) | >39 3/7 wk (n = 7565 ) | 40 0/7 –40 3/7 wk (n = 522) | >40 3/7 wk (n = 2933) | 41 0/7 –41 3/7 wk (n = 471) | >41 3/7 wk (n = 547) | |
| Male | 309 (48.4) | 3805 (50.3) | 271 (51.9) | 1517 (51.7) | 241 (51.2) | 285 (52.1) |
| Birthweight, g | 3416 ± 448 b | 3527 ± 461 | 3543 ± 443 b | 3591 ± 466 | 3645 ± 428 | 3600 ± 493 |
| 5-min Apgar score ≤5 | 2 (0.3) | 60 (0.8) | 4 (0.8) | 24 (0.8) | 2 (0.4) | 8 (1.4) |
| Umbilical artery pH ≤7.0 | 5/183 (2.7) | 58/3445 (1.7) | 5/169 (2.9) | 30/1417 (2.1) | 3/172 (1.7) | 6/294 (2.0) |
| Admission to NICU | 46 (7.2) | 703 (9.3) | 48 (9.2) | 309 (10.5) | 39 (8.3) | 64 (11.7) |
| Antepartum or intrapartum death | 0 | 9 (0.1) | 0 | 4 (0.1) | 0 | 4 (0.7) |
| Hypoxic-ischemic Encephalopathy | 0 | 5 (0.06) | 1 (0.2) | 2 (0.07) | 0 | 1 (0.2) |
| Neonatal death | 0 | 3 (0.04) | 0 | 1 (0.03) | 0 | 0 |
| Perinatal death a | 0 | 12 (0.1) | 0 | 5 (0.2) | 0 | 4 (0.7) |
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