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Published in final edited form as:

Am J Perinatol. 2022 April ; 39(5): 519–525. doi:10.1055/s-0040-1716711.

Labor Induction at 39 Weeks Compared with Expectant

Management in Low-Risk Parous Women
Stephen M. Wagner, MD1, Grecio Sandoval, MA2, William A. Grobman, MD, MBA3, Jennifer
L. Bailit, MD, MPH4, Ronald J. Wapner, MD5, Michael W. Varner, MD6, John M. Thorp Jr.,
MD7, Mona Prasad, DO, MPH8, Alan T. N. Tita, MD, PhD9, George R. Saade, MD10, Yoram
Sorokin, MD11, Dwight J. Rouse, MD12, Jorge E. Tolosa, MD, MSCE13, Eunice Kennedy
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Shriver National Institute of Child Health Human Development Maternal-Fetal Medicine

Units Network*
1Departmentsof Obstetrics and Gynecology, University of Texas Health Science Center at
Houston, McGovern Medical School-Children’s Memorial Hermann Hospital, Houston, Texas
2George Washington University Biostatistics Center, Washington, District of Columbia
3Departments of Obstetrics and Gynecology, Northwestern University, Chicago, Illinois
4MetroHealth Medical Center-Case Western Reserve University, Cleveland, Ohio
5Departments of Obstetrics and Gynecology, Columbia University, New York City, New York
6Departments of Obstetrics and Gynecology, University of Utah Health Sciences Center, Salt
Lake City, Utah
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7University of North Carolina at Chapel Hill, Chapel Hill, North Carolina

8Departments of Obstetrics and Gynecology, The Ohio State University, Columbus, Ohio
9Departments of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham,
Alabama
10University of Texas Medical Branch, Galveston, Texas
11Wayne State University, Detroit, Michigan
12Brown University, Providence, Rhode Island
13Oregon Health & Science University, Portland, Oregon
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Abstract

*See Supplementary Material (available in the online version) for the list of other members of the NICHD MFMU Network.
Address for correspondence Stephen M. Wagner, MD, Department of Obstetrics, Gynecology and Reproductive Sciences, McGovern
Medical School at The University of Texas Health Science Center at Houston, 6431 Fannin Street, MSB 3.286, Houston, TX 77030
(stephen.m.wagner@uth.tmc.edu).
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.
 Wagner et al. Page 2

Objective—Our objective was to compare outcomes among low-risk parous women who
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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%
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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
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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
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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

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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
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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
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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.
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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
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<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).

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Maternal demographics, clinical characteristics, and intrapartum outcomes were compared

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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
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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).

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)
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compared with those who were not electively induced (median [Q1–Q3]: 5.0 [2.0–8.0]
hours).

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.
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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).

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Discussion
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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
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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
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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
Refer to Web version on PubMed Central for supplementary material.

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.
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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.

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References
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of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU)
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5. Grobman WA, Rice MM, Reddy UMEunice Kennedy Shriver National Institute of Child Health
and Human Development Maternal–Fetal Medicine Units Network. , et al. Labor induction versus
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expectant management in low-risk nulliparous women. N Engl J Med 2018;379(06):513–523

[PubMed: 30089070]
6. Osmundson S, Ou-Yang RJ, Grobman WA. Elective induction compared with expectant
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8. Miller NR, Cypher RL, Foglia LM, Pates JA, Nielsen PE. Elective induction of labor compared with
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9. Hersh AR, Skeith AE, Sargent JA, Caughey AB. Induction of labor at 39 weeks of gestation versus
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10. Grobman WA, Sandoval G, Reddy UMEunice Kennedy Shriver National Institute of Child
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Health and Human Development Maternal-Fetal Medicine Units (MFMU) Network. , et al. Health
resource utilization of labor induction versus expectant management. Am J Obstet Gynecol
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156.e4 [PubMed: 19110225]
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of labor. Evid Rep Technol Assess (Full Rep) 2009;176:1–257
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expectant management: maternal and neonatal outcomes. Obstet Gynecol 2013;122(04):761–769
[PubMed: 24084532]
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15. Grobman WA, Bailit JL, Rice MMEunice Kennedy Shriver National Institute of Child Health and
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16. Sinkey RG, Blanchard CT, Szychowski JM, et al. Elective induction of labor in the 39th week of
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Key Points
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• 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.
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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).
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Table 1

Demographic characteristics of the study population

Elective induction (n = 2,648) Expectant management (n = 18,174) p-Value

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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

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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).</
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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
Wagner et al.

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

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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)
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Elective induction (n = 2,648) Expectant management (n = 18,174) OR (95% CI) aOR (95% CI)
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.
Wagner et al.

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.

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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
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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)

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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)
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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)
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.
Wagner et al.

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.

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