Abstract
Objective
Our objective was to compare outcomes among low-risk parous women who underwent elective labor induction at 39 weeks versus expectant management.
Study Design
This is a secondary analysis of an observational cohort of 115,502 mother–infant dyads who delivered at 25 hospitals between 2008 and 2011. The inclusion criteria for this analysis were low-risk parous women with nonanomalous singletons with at least one prior vaginal delivery after 20 weeks, who delivered at ≥390/7 weeks. Women who electively induced between 390/7 and 396/7 weeks were compared with women who expectantly managed ≥390/7 weeks. The primary outcome for this analysis was cesarean delivery. Secondary outcomes were composites of maternal adverse outcome and neonatal adverse outcome. Multivariable logistic regression was used to estimate adjusted odds ratios (aOR).
Results
Of 20,822 women who met inclusion criteria, 2,648 (12.7%) were electively induced at 39 weeks. Cesarean delivery was lower among women who underwent elective induction at 39 weeks than those who did not (2.4 vs. 4.6%, adjusted odds ratio [aOR]: 0.70, 95% confidence interval [CI]: 0.53–0.92). The frequency of the composite maternal adverse outcome was significantly lower for the elective induction cohort as well (1.6 vs. 3.1%, aOR: 0.66, 95% CI: 0.47–0.93). The composite neonatal adverse outcome was not significantly different between the two groups (0.3 vs. 0.6%; aOR: 0.60, 95% CI: 0.29–1.23).
Conclusion
In low-risk parous women, elective induction of labor at 39 weeks was associated with decreased odds of cesarean delivery and maternal morbidity, without an increase in neonatal adverse outcomes.
Keywords: elective induction, parous pregnancy, cesarean delivery, maternal morbidity
Of approximately 2.4 million parous women who delivered in the United States in 2017, over half were considered low risk (those without hypertensive disorder of pregnancy, diabetes, or other medical indication for delivery at 39 weeks).1,2 Renewed interest in the optimal timing of delivery in low-risk parous women is driven in part by the publication of the ARRIVE (A Randomized Trial of Induction Versus Expectant Management) trial.3,4 The ARRIVE trial provides evidence that low-risk nulliparous women have fewer cesarean deliveries and their neonates lower respiratory morbidity with elective induction at 39 weeks of gestational age versus expectant management.5 This result was a departure from previous observational studies of low-risk women that suggested elective induction at 39 weeks resulted in increased cesarean delivery rates without demonstrable perinatal benefit.6–8 Further analysis of elective induction at 39 weeks suggest that it is a cost-effective way of improving patient outcomes.9,10
However, there is paucity of information on the likelihood of cesarean delivery and maternal and neonatal morbidity among low-risk parous women who undergo elective induction of labor compared with those who are managed expectantly. Available observational data are limited by variations in comparison groups, outcomes measured, and single-site studies.2,11–14
Our primary objective was to compare the cesarean delivery rate among low-risk women with prior vaginal birth who were electively induced at 390/7 to 396/7 weeks versus expectant management at 39 weeks or beyond (i.e., regardless of whether labor was induced for medical reasons or spontaneous labor). We hypothesized that cesarean delivery would be reduced in women electively induced at 39 weeks.
Materials and Methods
This is a secondary analysis of the Assessment of Perinatal Excellence study, in which data were collected on randomly selected days between March 2008 and February 2011 at 25 hospitals in the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal–Fetal Medicine Units Network. Detailed methods from the original study have been published elsewhere.15 In brief, patients eligible for data collection were those who delivered within the institution, were at least 23 weeks of gestation, and had a live fetus on admission. Institutional review board approval was obtained at each participating institution under a waiver of informed consent.
Inclusion criteria for our secondary analysis included parous women (defined as having experienced at least one previous vaginal delivery at 200/7 weeks or beyond) with singleton gestations in cephalic presentation at 390/7 weeks or greater. In an effort to mimic the methodologic approach used by ARRIVE, our exclusion criteria consisted of the following: inadequate dating (no ultrasonography confirming or revising the estimated due date before 220/7 weeks), history of cesarean delivery, scheduled cesarean delivery, known major fetal anomaly, abnormal placentation, major maternal medical illnesses (including diabetes mellitus, lupus, cardiac disease, renal insufficiency, and hypertensive disorders of pregnancy diagnosed prior to 390/7 weeks), and heparin use in pregnancy.
Women who underwent elective induction between 390/7 and 396/7 were compared with women who were expectantly managed beyond 390/7 weeks. Given the potential overlap of exposure for parturient in the 39th week, a sensitivity analysis was performed in which eligible women undergoing elective inductions were compared with those who were expectantly managed and delivered at ≥400/7 weeks.
The primary outcome for this analysis was cesarean delivery. Secondary outcomes included a composite of maternal adverse outcomes and a composite of neonatal adverse outcomes. Composite maternal adverse outcomes included any of the following: suspectedor treated chorioamnionitis, 3 or 4 degrees laceration, deep venous thrombosis, pulmonary embolism, abruption, ICU admission, transfusion of blood products, wound infection, or death. Composite perinatal adverse outcomes consisted of any of the following: Apgar score <4 at 5 minutes, ventilator support, cardiopulmonary resuscitation, hypoxic ischemic encephalopathy, seizure, proven sepsis, bronchopulmonary dysplasia, persistent pulmonary hypertension, necrotizing enterocolitis class 2 or 3, intraventricular hemorrhage grade III or IV, fracture, neonatal brachial plexus palsy, facial nerve palsy, meconium aspiration, or perinatal death. Among the two groups, we also compared the length of time from admission to delivery, the rate of shoulder dystocia, and admission to the neonatal intensive care unit (NICU).
Maternal demographics, clinical characteristics, and intrapartum outcomes were compared between the two groups using Chi-square test or Fisher’s exact test for categorical variables and Wilcoxon’s rank sum test for continuous variables. Logistic regression models were used to estimate the association between exposure and binomial outcomes and generalized linear models were used to estimate the association between exposure and the time from admission to delivery. Models were adjusted for maternal age, body mass index (BMI), race ethnicity, neonatal sex, and hospital as a random effect. Statistical significance was defined as p <0.05 and all tests were two-tailed. No imputation for missing data was performed. All statistical analyses were performed with SAS (version 9.4).
Results
Of 115,502 mother–infant dyads in the initial study, 20,822 met the inclusion criteria for this secondary analysis (Fig. 1). The proportion of low-risk parous women who were electively induced at 390/7 to 396/7 weeks was 12.7% (n = 2,648). The women in the elective-induction group were more likely to be older, non-Hispanic white, have a lower BMI, and have private insurance (Table 1).
Fig. 1.
Flow diagram of study population. *Other complications include hypertension, pregestational or gestational diabetes, thrombophilia, anticoagulation use, previa or accreta, and reasons for hospital admission of vaginal bleeding/abruption, deep vein thrombosis, injury/trauma, asthma exacerbation, seizures, procedure, or other maternal medical condition (nonobstetrical).
Table 1.
Demographic characteristics of the study population
| Elective induction (n = 2,648) | Expectant management (n = 18,174) | p-Value | |
|---|---|---|---|
| Gestational age at delivery (wk) | 39.3 ± 0.29 | 40.1 ± 0.70 | <0.001 |
| Maternal age (y) | 30.1 ± 5.00 | 28.8 ± 5.56 | <0.001 |
| Race/ethnicity | <0.001 | ||
| Non-Hispanic White | 2,063 (77.9) | 6,906 (38.0) | |
| Non-Hispanic Black | 209 (7.9) | 3,571 (19.6) | |
| Hispanic | 208 (7.9) | 6,264 (34.5) | |
| Non-Hispanic Asian/other/unknown | 168 (6.3) | 1,433 (7.9) | |
| BMI (kg/m2) | 30.0 ± 5.29 | 31.1 ± 5.77 | <0.001 |
| BMI | <0.001 | ||
| < 25 kg/m2 | 378 (14.4) | 1,987 (11.2) | |
| 25–30 kg/m2 | 1,124 (42.9) | 6,612 (37.4) | |
| ≥30 kg/m2 | 1,115 (42.6) | 9,094 (51.4) | |
| Number of previous pregnancies | <0.001 | ||
| 1 | 887 (33.5) | 6,712 (36.9) | |
| 2 | 771 (29.1) | 5,302 (29.2) | |
| 3 | 495 (18.7) | 3,108 (17.1) | |
| > 3 | 495 (18.7) | 3,052 (16.8) | |
| Private insurance | 2,028 (77.0) | 7,194 (39.9) | <0.001 |
| Cigarette used during this pregnancy | 167 (6.3) | 1,693 (9.3) | <0.001 |
| Alcoholic drinks during this pregnancy | 78 (2.9) | 478 (2.6) | 0.35 |
| Birthweight (g) | 3,458 ± 374.5 | 3,517 ± 428.1 | <0.001 |
Abbreviation: BMI, body mass index.
Notes: Data presented as n (%) or mean ± standard deviation. Statistically significant values are bolded.
Number of missing values: BMI (n = 512), insurance status (n = 137), cigarette use (n = 15), alcohol use (n = 25), and birthweight (n = 7).</
The primary outcome of cesarean delivery was lower among women who underwent elective induction than in those who did not (2.4 vs. 4.6%, adjusted odds ratio [aOR]: 0.70, 95% confidence interval [CI]: 0.53–0.92, Table 2). The composite maternal adverse outcome was lower in the elective induction group as well (1.6 vs. 3.1%, aOR: 0.66, 95% CI: 0.47–0.93, Table 2). Rates of shoulder dystocia was also significantly lower in the elective induction cohort (3.1 vs. 3.4%, aOR: 0.69, 95% CI: 0.53–0.89, Table 2). The time from admission to delivery was longer (adjusted mean difference 2.4 hours, 95% CI: 2.1–2.7 hours) for women who underwent elective induction of labor (median [Q1–Q3]: 7.0 [5.0– 10.0] hours) compared with those who were not electively induced (median [Q1–Q3]: 5.0 [2.0–8.0] hours).
Table 2.
Outcomes of low-risk parous women undergoing elective induction at 39 weeks of gestation and all other low-risk parous deliveries from 39 to 42 weeks of gestation
| Elective induction (n = 2,648) | Expectant management (n = 18,174) | OR (95% CI) | aOR (95% CI) | |
|---|---|---|---|---|
| Cesarean delivery | 63 (2.4) | 840 (4.6) | 0.50 (0.39–0.65) | 0.70 (0.53–0.92) |
| Composite maternal morbidity | 42 (1.6) | 569 (3.1) | 0.50 (0.36–0.68) | 0.66 (0.47–0.93) |
| 3 or 4 degrees laceration | 17 (0.6) | 181 (1.0) | ||
| Abruption | 2 (0.1) | 24 (0.1) | ||
| Admission to ICU | 4 (0.2) | 24 (0.1) | ||
| Suspected or treated for chorioamnionitis | 12 (0.5) | 253 (1.4) | ||
| Thromboembolism | 0 | 2 (0.01) | ||
| Transfusion | 13 (0.5) | 116 (0.6) | ||
| Wound cellulitis | 1 (0.04) | 4 (0.02) | ||
| Death | 0 | 0 | ||
| Composite perinatal morbidity | 9 (0.3) | 102 (0.6) | 0.60 (0.31–1.20) | 0.60 (0.29–1.23) |
| Apgar score <4 | 0 | 15 (0.1) | ||
| Brachial plexus palsy | 0 | 15 (0.1) | ||
| Bronchopulmonary dysplasia | 0 | 1 (0.01) | ||
| Cardiopulmonary resuscitation | 1 (0.04) | 3 (0.02) | ||
| Facial nerve palsy | 0 | 1 (0.01) | ||
| Fracture | 1 (0.04) | 9 (0.05) | ||
| HIE | 1 (0.04) | 14 (0.1) | ||
| IVH grade 3 or 4 | 0 | 0 | ||
| Meconium aspiration | 0 | 23 (0.1) | ||
| NEC stage 2 or 3 | 0 | 0 | ||
| Persistent pulmonary hypertension | 1 (0.04) | 13 (0.1) | ||
| Seizure | 1 (0.04) | 6 (0.03) | ||
| Proven sepsis | 0 | 12 (0.1) | ||
| Ventilator support | 7 (0.3) | 32 (0.2) | ||
| Perinatal death | 0 | 3 (0.02) | ||
| Shoulder dystocia | 82 (3.1) | 622 (3.4) | 0.90 (0.71–1.14) | 0.69 (0.53–0.89) |
| NICU admission | 96 (3.6) | 647 (3.6) | 1.02 (0.82–1.27) | 0.80 (0.62–1.01) |
Abbreviations: aOR, adjusted odds ratio; CI, confidence interval; HIE, hypoxic ischemic encephalopathy; ICU, intensive care unit; IVH, intraventricular hemorrhage; NEC, necrotizing enterocolitis; NICU, neonatal intensive care unit; OR, odds ratio.
Notes: Data presented as n (%), unless otherwise noted. Statistically significant values are bolded.
Odds adjusted for maternal age, race/ethnicity, BMI, neonatal sex, and hospital as a random effect.
The rate of NICU admissions did not differ between groups (3.6 vs. 3.6%, aOR: 0.80, 95% CI: 0.62–1.01). The composite perinatal adverse outcomes was not statistically different between groups (0.3 vs. 0.6%, aOR: 0.60, 95% CI: 0.29–1.23, Table 2). In the women who underwent elective induction, there were no perinatal deaths, while women who underwent expectant management had three perinatal deaths (p-value = 1.00).
In the sensitivity analysis, results were overall similar to the primary analysis. There was a statistical difference between women who underwent 39-week elective induction and those who were expectantly managed beyond 40 0/7 weeks in cesarean delivery (2.4 vs. 5.5%, aOR: 0.59, 95% CI: 0.44–0.80, Table 3), composite maternal adverse outcomes (1.6 vs. 3.4%, aOR: 0.65, 95% CI: 0.45–0.92, Table 3), and the time from admission to delivery (median [Q1–Q3]: 7.0 [5.0, 10.0] vs. 6.0 [3.0–9.0], adjusted mean difference 1.8 hours, and 95% CI: 1.4–2.2 hours). As before, there was no statistical difference in composite neonatal adverse outcomes (0.3 vs. 0.6%, aOR: 0.70, 95% CI: 0.34–1.48, Table 3).
Table 3.
Sensitivity analysis of low-risk parous women undergoing elective induction at 39 weeks of gestation and low-risk parous women who delivered at 400/7 to 422/7 weeks of gestation
| Elective induction 390/7 to 396/7 (n = 2,648) | Other deliveries 400/7 to 422/7 (n = 10,044) | OR (95% CI) | aOR (95% CI) | |
|---|---|---|---|---|
| Cesarean delivery | 63 (2.4) | 551 (5.5) | 0.42 (0.32–0.55) | 0.59 (0.44–0.80) |
| Composite maternal morbidity | 42 (1.6) | 344 (3.4) | 0.45 (0.33–0.63) | 0.65 (0.45–0.92) |
| 3 or 4 degrees laceration | 17 (0.6) | 107 (1.1) | ||
| Abruption | 2 (0.1) | 13 (0.1) | ||
| Admission to ICU | 4 (0.2) | 12 (0.1) | ||
| Suspected or treated for chorioamnionitis | 12 (0.5) | 154 (1.5) | ||
| Thromboembolism | 0 | 1 (0.01) | ||
| Transfusion | 13 (0.5) | 74 (0.7) | ||
| Wound cellulitis | 1 (0.04) | 2 (0.02) | ||
| Death | 0 | 0 | ||
| Composite neonatal morbidity | 9 (0.3) | 57 (0.6) | 0.60 (0.30–1.21) | 0.70 (0.34–1.48) |
| Apgar score <4 | 0 | 8 (0.1) | ||
| Brachial plexus palsy | 0 | 10 (0.1) | ||
| Bronchopulmonary dysplasia | 0 | 0 | ||
| Cardiopulmonary resuscitation | 1 (0.04) | 0 | ||
| Facial nerve palsy | 0 | 1 (0.01) | ||
| Fracture | 1 (0.04) | 6 (0.1) | ||
| HIE | 1 (0.04) | 9 (0.1) | ||
| IVH grade 3 or 4 | 0 | 0 | ||
| Meconium aspiration | 0 | 12 (0.1) | ||
| NEC stage 2 or 3 | 0 | 0 | ||
| Persistent pulmonary hypertension | 1 (0.04) | 6 (0.1) | ||
| Seizure | 1 (0.04) | 2 (0.02) | ||
| Proven sepsis | 0 | 4 (0.04) | ||
| Ventilator support | 7 (0.3) | 11 (0.1) | ||
| Perinatal death | 0 | 2 (0.02) | ||
| Shoulder dystocia | 82 (3.1) | 397 (4.0) | 0.78 (0.61–0.99) | 0.60 (0.45–0.80) |
| NICU admission | 96 (3.6) | 370 (3.7) | 0.98 (0.78–1.24) | 0.88 (0.67–1.15) |
Abbreviations: aOR, adjusted odds ratio; CI, confidence interval; HIE, hypoxic ischemic encephalopathy; ICU, intensive care unit; IVH, intraventricular hemorrhage; NEC, necrotizing enterocolitis; NICU, neonatal intensive care unit; OR, odds ratio.
Notes: Data presented as n (%), unless otherwise noted. Statistically significant values are bolded.
Odds adjusted for maternal age, race/ethnicity, BMI, neonatal sex, and hospital as a random effect.
Discussion
This secondary analysis of an observational study showed elective induction of labor in low-risk parous women at 39 weeks compared with expectant management was associated with significantly lower odds of cesarean delivery and of composite maternal adverse outcomes. The difference between groups in the adverse perinatal outcome did not reach statistical significance. These findings are consistent with those of a randomized controlled trial that examined 39-week elective induction in low-risk nulliparous women.5 Single-site observational studies have also demonstrated the lower chance of cesarean delivery, as well as a lower chance of adverse perinatal outcomes, in low-risk parous women who undergo elective induction of labor at 39 weeks of gestation.16,17
Strength of this analysis was the large sample size of over 20,000 ethnically diverse mother–infant dyads who delivered at 25 different hospitals. By including geographically dispersed academic and community hospitals, the generalizability of this study is improved, although most hospitals were teaching hospitals. A weakness of this analysis is its observational nature. Because this was not a randomized trial, we cannot be certain whether some women who would have planned to be electively induced in the 39th week instead had spontaneous labor or development of a medical indication for induction, and were categorized in the expectant-management group in the primary analysis. The sensitivity analysis, which reduces the potential for misclassification, further confirms our findings. Also, the two study groups differed in baseline characteristics, and while we attempted to adjust for known differences in multivariable analysis, the possibility of omitted variable bias remains.
In conclusion, elective induction of labor at 39 weeks was associated with decreased frequency of cesarean delivery and maternal morbidity in low-risk parous women. These data can be utilized in a shared decision-making process when discussing 39-week elective induction with low-risk parous women and are useful in planning a randomized trial to determine whether induction at 39 weeks, without other medical indication, improves outcomes in parous women.
Supplementary Material
Key Points.
39-week elective induction is associated with decreased cesarean delivery in low-risk parous women.
Compared with expectant management, maternal adverse outcomes were lower with elective induction.
Neonatal adverse outcomes are unchanged between elective and expectant management groups.
Acknowledgments
The authors thank Cynthia Milluzzi, RN, and Joan Moss, RNC, MSN, for protocol development and coordination between clinical research centers and Elizabeth Thom, PhD, Madeline M. Rice, PhD, Brian M. Mercer, MD, Uma M. Reddy, MD, MPH, and Catherine Y. Spong, MD, for protocol development and oversight.
Funding
The project described was supported by grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (HD21410, HD27869, HD27915, HD27917, HD34116, HD34208, HD36801, HD40500, HD40512, HD40544, HD40545, HD40560, HD40485, HD53097, and HD53118). The National Center for Research Resources (UL1 RR024989 and 5UL1 RR025764). Comments and views of the authors do not necessarily represent views of the National Institutes of Health.
Footnotes
See Supplementary Material (available in the online version) for the list of other members of the NICHD MFMU Network.
Note
This study was presented in part at the 40th annual meeting of the Society for Maternal–Fetal Medicine, February 3 to 8, 2020, Grapevine, TX.
Conflict of Interest
None declared.
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