Background
Bariatric surgery is a widely used treatment option for obesity that often provides long-term weight control and health benefits. Although a growing number of women are becoming pregnant after bariatric surgery, only a few population-based studies have assessed the impact thereof on perinatal outcomes.
Objective
This study aimed to examine the association between bariatric surgery and adverse perinatal outcomes in pregnant women and to examine whether the risk for adverse perinatal outcomes is modified by the postsurgery weight, gestational weight gain, type of bariatric surgery, timing of pregnancy after bariatric surgery, and maternal comorbidities.
Study Design
A retrospective cohort study was performed with the use of the Bariatric Surgery Registry and hospital inpatient and outpatient physician encounter records. The International Classification of Diseases, Ninth and Tenth Revision codes from hospitalizations during pregnancy and infant birth records were used to ascertain the outcomes of interest. Women eligible for BS who delivered at ≥20 weeks of gestation (n=20,213) at Kaiser Permanente Southern California hospitals (January 1, 2007 to December 31, 2018) were included in the study. Adjusted odds ratios were derived from logistic regression models with inverse probability of treatment weighting to adjust for confounding using propensity scores.
Results
Bariatric surgery was associated with a reduction in the risks for gestational diabetes (adjusted odds ratio, 0.60; 95% confidence interval, 0.53–0.69; P <.001), preeclampsia (adjusted odds ratio, 0.53; 95% confidence interval, 0.46–0.61; P <.001), chorioamnionitis (adjusted odds ratio, 0.45; 95% confidence interval, 0.32–0.63; P <.001), cesarean delivery (adjusted odds ratio, 0.65; 95% confidence interval, 0.59–0.72; P <.001), large for gestational age neonate (adjusted odds ratio, 0.23; 95% confidence interval, 0.19–0.29; P <.001), macrosomia (adjusted odds ratio, 0.24; 95% confidence interval, 0.19–0.30; P <.001), and neonatal intensive care unit admission (adjusted odds ratio, 0.70; 95% confidence interval, 0.61–0.81; P <.001). However, bariatric surgery was also associated with a significantly increased risk for small for gestational age neonates (adjusted odds ratio, 2.46; 95% confidence interval, 2.16–2.79; P <.001). The risk for the adverse outcomes is independent of the time interval between the surgery and subsequent pregnancy.
Conclusion
These data suggest that there are many pregnancy outcome benefits for women with severe obesity who undergo bariatric surgery; however, women who have undergone bariatric surgery before pregnancy should be monitored closely to reduce the risk for small for gestational age neonates and postpartum hemorrhage.
Introduction
Obesity is a major public health problem affecting all ages, races and ethnicities, and socioeconomic classes. In the United States, the prevalence of severe obesity (body mass index [BMI] ≥35 kg/m 2 ) among women increased from 7.3% in the period spanning 2007 to 2008 to 9.7% in the period spanning 2015 to 2016. African American and Hispanic women are affected disproportionately more by the condition than non-Hispanic White and Asian women. This rise in prevalence has been accompanied by a continued increase in obesity-related comorbidities and medical costs. ,
Maternal obesity increases the risk for metabolic and cardiovascular illness, impairs fertility, reduces life expectancy, and is associated with several adverse pregnancy outcomes, including preeclampsia, gestational diabetes mellitus (GDM), postpartum hemorrhage, cesarean delivery, excess fetal growth, stillbirth, congenital anomalies, and neonatal death. The most effective treatment for women with severe obesity is bariatric surgery (BS). , Recent studies suggest that treatment of women with severe obesity using BS may reduce the risks for GDM, preeclampsia, and macrosomia. , However, crucial questions remain unanswered about the impact of BS on other pre- and postnatal adverse outcomes. Furthermore, the impact of factors such as postsurgery BMI, gestational weight gain (GWG), BS type, timing of pregnancy after BS, and maternal comorbidities on pregnancy outcomes has not been fully elucidated. We aimed to examine the association between BS and the risk for adverse perinatal outcomes in pregnant women and to examine if the risk is modified by the prepregnancy weight, GWG, type of BS, timing of pregnancy after a BS, and maternal comorbidities.
Why was this study conducted?
There is lack of data on the benefits of bariatric surgery (BS) and pregnancy outcomes in racial minorities. This study aimed to assess whether the magnitude of the association between BS and pregnancy outcomes was modified by surgery type, postsurgery obesity, timing of the pregnancy, or comorbidities.
Key findings
BS was associated with a reduction in the risk for preeclampsia, gestational diabetes, macrosomia, chorioamnionitis, cesarean delivery, neonatal intensive care unit (NICU) admission, and surgical site infection. BS was also associated with an increased risk for small for gestational age neonates and postpartum hemorrhage. Some variation was found in the investigated outcomes across racial and ethnic backgrounds.
What does this add to what is known?
We evaluated patients who underwent a vertical sleeve gastrectomy, the most prevalent surgical procedure used in the United States. We found that BS may decrease the odds of NICU admission by almost 40%. BS is associated with increased postpartum hemorrhage risk regardless of the delivery mode, prepregnancy body mass index, and race and ethnicity. A sizable reduction in the risk for surgical site infection was found. Our large sample size permitted subgroup analyses based on race and ethnicity categories.
Materials and Methods
This population-based, retrospective cohort study utilized electronic health records (EHR) of pregnant women receiving obstetrical care in 15 Kaiser Permanente Southern California (KPSC) hospitals and 234 outpatient clinics between January 1, 2007, and December 31, 2018 (n=434,881). We compared pregnant women who underwent BS at any time before pregnancy with pregnant women who were eligible for BS but who were not recorded as having undergone BS in the KPSC Bariatric Registry. The study received institutional review board approval with exemption of informed consent.
Of the 434,881 pregnancies reported over the study period, 414,668 pregnancies were excluded for the following reasons: non-KPSC members for at least 90 days during pregnancy, women <18 years old, pregnancies lasting <20 weeks, multifetal gestations, missing data on prepregnancy weight and height, and women who did not undergo BS with prepregnancy BMI <35 kg/m 2 , leaving 20,213 women who delivered a subsequent singleton pregnancy for analyses ( Supplemental Figure ). Pregnancies lasting <20 weeks were excluded because it was markedly underreported in the database used for this study and may have biased the analysis.
Details about the BS procedures were obtained from the KPSC Bariatric Surgery Registry. All BS types were included in the analyses including the 2 most common operations (Roux-en-Y gastric bypass [RYGB] and vertical sleeve gastrectomy [VSG]) and other procedures (adjustable gastric band, vertical banded gastroplasty [VBG], and biliopancreatic diversion with duodenal switch).
KPSC patient eligibility for BS is based on the following National Institutes of Health Consensus Statement eligibility criteria: (1) a BMI ≥40 kg/m 2 with no comorbidities or (2) a BMI between 35 and 40 kg/m 2 in the presence of certain obesity-related comorbidities (eg, diabetes mellitus and severe sleep apnea). Women who are pregnant at the time of surgical consult and those who are smoking at the time of evaluation for surgery are not allowed to proceed to BS. Furthermore, a patient may be deemed ineligible for BS if the surgeon decides that the procedure is not in the patient’s best interest for other reasons.
International Classification of Diseases, Ninth and Tenth Revision codes, as recorded in the EHRs, were used to ascertain the maternal medical and obstetrical conditions in addition to infant outcomes ( Supplemental Table 1 ). Details regarding the validation of these codes have been published previously. , Outcomes that were examined in this study were GDM; preeclampsia and eclampsia; placenta previa; placental abruption (a premature separation of the normally implanted placenta); abnormal fetal heart rate (FHR) tracings were identified as nonreassuring intrapartum patterns, consistent with the American College of Obstetricians and Gynecologists (ACOG) definitions of category II and category III electronic fetal monitoring tracings; premature rupture of membranes (PROM); preterm birth (PTB) and its subtypes (spontaneous [sPTB] and indicated [iPTB]); chorioamnionitis (an inflammation at the maternal-fetal interface); cesarean delivery; postpartum hemorrhage (blood loss >500 mL after a vaginal delivery or >1000 mL after a cesarean delivery); surgical site infection (SSI); small for gestational age (SGA) neonate; large for gestational age (LGA) neonate; macrosomia (birthweight ≥4500 g); stillbirth (the death of a fetus at ≥20 weeks’ gestation); Apgar score of <7 at 5 minutes; neonatal intensive care unit (NICU) admission; and respiratory distress syndrome (RDS). SGA and LGA neonates were defined as neonates with birthweights that are <10th and >90th percentile, respectively, based on race-, ethnicity-, and sex-specific birthweights for gestational age cutoffs (internal standard).
Potential determinants or confounders were obtained from the EHRs and categorized on the basis of previous knowledge and literature including maternal age (18–24, 25–29, 30–34, and ≥35 years), race and ethnicity (non-Hispanic White [White], non-Hispanic Black [Black], Hispanic, Asian or Pacific Islander, and other or mixed groups), education (<12, 12, and ≥13 years of completed schooling), timing of prenatal care initiation (early or first-trimester care initiation and no or late care), self-reported prenatal smoking (yes or no), prepregnancy BMI (calculated as weight [kg] divided by the squared height [m 2 ] and was categorized as 18.5–24.9, 25.0–29.9, 30.0–34.9, 35.0–39.9, 40.0–44.9, and ≥45), maternal medical comorbidities (chronic hypertension and pregestational diabetes), and gestational age that was calculated from the date of the last menstrual period (LMP) and corroborated by early pregnancy ultrasonography. If the date of the LMP was unknown or if disagreement was found between the dates estimated from the LMP and sonogram, the date generated from the latter was used. Information on the median family household income was based on the census tract of residence (<$29,999, $30,000–$49,000, $50,000–$69,999, $70,000–$89,999, and ≥$90,000). The interval between BS and the start of a subsequent pregnancy (<1, 1–1.5, 1.5–2, and ≥2 years) was estimated. GWG, based on the women’s prepregnancy BMIs, was used as per the Institute of Medicine recommendation. The recommended weight gain during pregnancy for women with a BMI of <19.8, 19.8 to 26.0, and 26.1 to 29.0 were 28 to 40, 25 to 35, and 15 to 25 lb, respectively. Women with a BMI >29 are advised to gain at least 15 lb during the course of their pregnancy (recommended range, 15–25 lb).
Statistical analyses were performed using SAS version 9.4 (SAS Institute, Cary, NC). We examined the distribution of maternal characteristics by BS status. For categorical variables, frequencies and percentages were estimated for each level and the distribution of each variable was compared using chi-square statistics. For continuous variables, the means were estimated and compared using t tests. Logistic regression analysis was conducted to estimate the crude odds ratios (ORs) for post-BS perinatal outcomes, reported as point estimates with 95% confidence intervals (CIs). Adjusted ORs (aORs) were estimated using logistic regression models with inverse probability of treatment weighting (IPTW) using the propensity score to adjust for confounding. A logistic regression model was used to calculate the propensity scores. Variables in the propensity score model included age, race and ethnicity, education, median household income, prenatal care, parity, smoking during pregnancy, GWG, maternal medical comorbidities, and history of the outcome ( Table 1 ). Because the time interval between BS and pregnancy, the prepregnancy BMI, maternal comorbidities, race and ethnicity, and BS type may potentially modify the association between BS, other factors, and adverse pre- and postnatal outcomes, , , we repeated the analysis on each subset stratified by these factors. Inclusion of GWG in the model as a categorical variable may have affected our outcomes. Therefore, to further verify whether our findings still hold true, we performed a sensitivity analysis after modeling GWG as a continuous variable in the regression models. All statistical tests were 2-sided and statistical significance was defined as P <.05.
| Maternal characteristic | Number of pregnancies (N=20,213) | BS status | P value a | |
|---|---|---|---|---|
| No-BS, n=18,327 (%) | BS, n=1886 (%) | |||
| Age (y), mean (SD) | 31.3 (5.3) | 31.1 (5.3) | 33.1 (5.0) | <.001 |
| Age category (y) | <.001 | |||
| 18–24 | 2283 | 2184 (11.9) | 99 (5.3) | |
| 25–29 | 5366 | 5004 (27.3) | 362 (19.2) | |
| 30–34 | 6753 | 6099 (33.3) | 654 (34.7) | |
| ≥35 | 5811 | 5040 (27.5) | 771 (40.9) | |
| Race and ethnicity | <.001 | |||
| Non-Hispanic White | 3849 | 3454 (18.9) | 395 (20.9) | |
| Non-Hispanic Black | 2939 | 2636 (14.4) | 303 (16.1) | |
| Hispanic | 12,185 | 11,095 (60.5) | 1090 (57.8) | |
| Asian or Pacific Islander | 655 | 632 (3.5) | 23 (1.2) | |
| Other or multiple | 489 | 423 (2.3) | 66 (3.5) | |
| Education (y) | <.001 | |||
| <12 | 773 | 721 (3.9) | 52 (2.8) | |
| 12 | 6123 | 5652 (30.8) | 471 (25.0) | |
| ≥13 | 12,828 | 11,516 (62.8) | 1312 (69.6) | |
| Missing | 489 | 438 (2.4) | 51 (2.7) | |
| Median household income b | .427 | |||
| <$30,000 | 1458 | 1343 (7.3) | 115 (6.1) | |
| $30,000–$49,999 | 7396 | 6706 (36.6) | 690 (36.6) | |
| $50,000–$69,999 | 6560 | 5934 (32.4) | 626 (33.2) | |
| $70,000–$89,999 | 3129 | 2836 (15.5) | 293 (15.5) | |
| ≥$90,000 | 1648 | 1487 (8.1) | 161 (8.5) | |
| Nullipara | 6865 | 6197 (33.8) | 668 (35.4) | .373 |
| Late initiation or no PNC c | 1545 | 1434 (7.8) | 111 (5.9) | .001 |
| Smoking during pregnancy | 1350 | 1257 (6.9) | 93 (4.9) | .014 |
| Prepregnancy BMI (kg/m 2 ), mean (SD) | 42.3 (5.5) | 43.1 (4.8) | 35.0 (6.8) | <.001 |
| 18.5–24.9 | 82 | 0 (0.0) | 82 (4.4) | |
| 25.0–29.9 | 386 | 0 (0.0) | 386 (20.5) | |
| 30.0–34.9 | 549 | 0 (0.0) | 549 (29.1) | |
| 35.0–39.9 | 3897 | 3456 (18.9) | 441 (23.4) | |
| 40.0–44.9 | 10,145 | 9889 (54.0) | 256 (13.6) | |
| ≥45 | 5154 | 4982 (27.2) | 172 (9.1) | |
| Gestational weight gain (lb) d , mean (SD) | 10.2 (27.4) | 9.2 (27.5) | 19.7 (24.5) | <.001 |
| Under IOM guideline | 8837 | 8267 (45.1) | 570 (30.2) | |
| Within IOM guideline | 4130 | 3753 (20.5) | 377 (20.0) | |
| Over IOM guideline | 7006 | 6100 (33.3) | 906 (48.0) | |
| Missing | 240 | 207 (1.1) | 33 (1.8) | |
| Presence of comorbidities | ||||
| Chronic hypertension | 5207 | 4901 (26.7) | 306 (16.2) | <.001 |
| Pregestational diabetes | 2748 | 2534 (13.8) | 214 (11.4) | .003 |
| Timing of pregnancy after BS e | <.001 | |||
| <12 mo | 372 | N/A | 372 (19.7) | |
| 12–17 mo | 270 | N/A | 270 (14.3) | |
| 18–23 mo | 219 | N/A | 219 (11.6) | |
| ≥24 mo | 1025 | N/A | 1025 (54.4) | |
a P values for the difference in proportions between each categorical variable based on BS status were compared using chi-square statistics. For continuous variables, the means were compared using t tests
b Median family household income based on census tract of residence
c Late initiation or no PNC is care initiation after the first trimester or no prenatal care
d Gestational weight gain categories were created according to the IOM’s recommended weight gain during pregnancy and grouped into 3 categories (under, within, over the IOM recommendation). The recommended gestational weight gain for women with a BMI of <19.8, 19.8 to 26.0, or 26.1 to 29.0 are 28 to 40, 25 to 35, and 15 to 25 lb, respectively. Women with a BMI of >29 are advised to gain at least 15 lb during the course of their pregnancy (recommended range, 15–25 lb)
e Interval between BS procedure and the start of a subsequent pregnancy.
Results
Among the 20,213 eligible women who became pregnant, the prevalence of BS was 9.3% (n=1886). In the non-BS group and the BS group, the mean (standard deviation [SD]) ages were 31.1 (5.3) and 33.1 (5.0) years, respectively, the mean (SD) BMIs were 43.1 (4.8) and 35.0 (6.8) kg/m 2 , respectively, and the mean (SD) GWG were 9.2 (27.5) and 19.7 (24.5) lb, respectively ( Table 1 ). The corresponding P values were statistically significant at <.001 for each of these comparisons. Compared with women who did not undergo BS, women who underwent BS were more likely to be older, have completed ≥13 years of education, be nulliparous, and less likely to have late initiation or no prenatal care or to smoke during pregnancy. Among those who had the surgery, a greater proportion were of White and Black race than among those who did not have the surgery. Among the women who underwent BS, 54.0% became pregnant after the second year following their surgery. Women who did not undergo BS had higher rates of chronic hypertension and pregestational diabetes than those who underwent BS (26.7% vs 16.2%; P <.001 and 13.8% vs 11.4%; P =.003 respectively).
After adjusting for potential confounders ( Table 2 ), pregnancies after BS were associated with a reduced risk for GDM (aOR, 0.60; 95% CI, 0.53–0.69; P <.001), preeclampsia and eclampsia (aOR, 0.53; 95% CI, 0.46–0.61; P <.001), chorioamnionitis (aOR, 0.45; 95% CI, 0.32–0.63; P <.001), cesarean delivery (aOR, 0.65; 95% CI, 0.59–0.72; P <.001), LGA neonate (aOR, 0.23; 95% CI, 0.19–0.29; P <.001), macrosomia (aOR, 0.24; 95% CI, 0.19–0.30; P <.001), and NICU admission (aOR, 0.70; 95% CI, 0.61–0.81; P <.001) when compared with pregnancies among women who did not undergo BS. A pregnancy after BS was associated with an increased risk for an SGA neonate (aOR, 2.46; 95% CI, 2.16–2.79; P <.001) and postpartum hemorrhage (aOR, 1.79; 95% CI, 1.30–2.46; P <.001) when compared with pregnancies among women who did not undergo BS. Statistical analyses pertaining to chorioamnionitis, postpartum hemorrhage, and SSI were further adjusted for mode of delivery to account for the modifying effect of vaginal vs cesarean delivery. No statistically significant difference was observed between the BS and no-BS groups in other adverse outcomes.
| Adverse perinatal outcomes | Women without BS, n=18,327 (%) | Women with BS, n=1886 (%) | Odds ratios (95% confidence intervals) | ||
|---|---|---|---|---|---|
| Crude | a Adjusted | b P value | |||
| Gestational diabetes c | 4168 (26.4) | 294 (17.6) | 0.60 (0.52–0.68) | 0.60 (0.53–0.69) | <.001 |
| Preeclampsia and eclampsia | 4131 (22.5) | 199 (10.6) | 0.41 (0.35–0.47) | 0.53 (0.46–0.61) | <.001 |
| Placenta previa | 623 (3.4) | 80 (4.2) | 1.26 (0.99–1.60) | 1.17 (0.91–1.49) | .221 |
| Placental abruption | 168 (0.9) | 27 (1.4) | 1.57 (1.04–2.36) | 1.32 (0.85–2.05) | .219 |
| Abnormal fetal heart rate pattern | 5029 (27.4) | 563 (29.9) | 1.13 (1.01–1.25) | 1.05 (0.94–1.16) | .410 |
| Premature rupture of membranes | 1129 (6.2) | 121 (6.4) | 1.04 (0.86–1.27) | 0.89 (0.72–1.09) | .255 |
| PTB at <37 wk gestation | 2158 (11.8) | 208 (11.0) | 0.93 (0.80–1.08) | 0.99 (0.85–1.15) | .918 |
| Spontaneous PTB | 671 (3.7) | 72 (3.8) | 1.04 (0.81–1.33) | 1.04 (0.81–1.34) | .743 |
| Medically indicated PTB | 1487 (8.1) | 136 (7.2) | 0.88 (0.74–1.06) | 0.96 (0.81–1.15) | .736 |
| Chorioamnionitis d | 766 (4.2) | 46 (2.4) | 0.57 (0.42–0.77) | 0.45 (0.32–0.63) | <.001 |
| Cesarean delivery | 9341 (51.0) | 783 (41.5) | 0.68 (0.62–0.75) | 0.65 (0.59–0.72) | <.001 |
| Postpartum hemorrhage d , e | 254 (1.4) | 44 (2.3) | 1.70 (1.23–2.35) | 1.79 (1.30–2.46) | <.001 |
| Surgical site infection d | 229 (1.3) | 14 (0.7) | 0.59 (0.34–1.02) | 0.70 (0.43–1.17) | .174 |
| Small for gestational age neonate | 1520 (8.3) | 313 (16.6) | 2.20 (1.93–2.51) | 2.46 (2.16–2.79) | <.001 |
| Large for gestational age neonate | 3326 (18.2) | 109 (5.8) | 0.28 (0.23–0.34) | 0.23 (0.19–0.29) | <.001 |
| Macrosomia | 2944 (16.1) | 100 (5.3) | 0.29 (0.24–0.36) | 0.24 (0.19–0.30) | <.001 |
| Stillbirth | 126 (0.7) | 17 (0.9) | 1.31 (0.79–2.19) | 0.87 (0.48–1.59) | .769 |
| Apgar score <7 at 5 min | 245 (1.3) | 35 (1.9) | 1.40 (0.98–2.00) | 1.26 (0.87–1.82) | .255 |
| NICU admission | 3067 (16.7) | 236 (12.5) | 0.71 (0.62–0.82) | 0.70 (0.61–0.81) | <.001 |
| Respiratory distress syndrome | 1017 (5.6) | 90 (4.8) | 0.85 (0.68–1.06) | 0.88 (0.71–1.10) | .258 |
a Adjusted odds ratios were estimated using regression models with propensity score inverse probability of treatment weighting (IPTW). Variables in the propensity score model included age, race and ethnicity, education, median household income, prenatal care, parity, smoking during pregnancy, gestational weight gain (reference within the IOM guideline), maternal medical comorbidities, and a history of the outcome
b P values are from multivariable models used to estimate adjusted odds ratios
c Pregestational diabetes was excluded from variables in the propensity score model
d Further adjusted for route of delivery
e Information on postpartum hemorrhage requiring blood transfusion came from blood transfusion data extracted from electronic health records.
The number and rate of adverse perinatal outcomes differed with the length of the time interval between BS and a subsequent pregnancy ( Table 3 ). However, the benefits of BS on pregnancy outcomes was greater regardless of the interval between BS and a subsequent pregnancy ( Tables 3 and 4 ). The association between BS and an increased risk for SGA neonates observed in our study also seems to not be dependent on the time interval between BS and a subsequent pregnancy. However, a pregnancy in the period between 1 and 1.5 years or ≥2 years after surgery (aOR, 4.18; 95% CI, 2.44–7.17; P <.001 and aOR, 1.97; 95% CI, 1.32–2.93; P =.001, respectively) was associated with an increased risk for postpartum hemorrhage. A pregnancy ≥2 years after BS was associated with PTB (aOR, 1.29; 95% CI, 1.08–1.54; P =.006), an effect that was largely driven by iPTB (aOR, 1.33; 95% CI, 1.08–1.63; P =.008).
| Adverse perinatal outcomes in post-BS pregnancies | No-BS, n=18,327 (%) | Bariatric surgery | a P value | |||
|---|---|---|---|---|---|---|
| <1 y n=372 (%) | 1–1.5 y n=270 (%) | 1.5–2 y n=219 (%) | ≥2 y n=1025 (%) | |||
| Gestational diabetes b | 4168 (26.4) | 42 (12.8) | 31 (13.0) | 26 (13.1) | 195 (21.5) | <.001 |
| Preeclampsia or eclampsia | 4131 (22.5) | 42 (11.3) | 22 (8.2) | 16 (7.3) | 119 (11.6) | <.001 |
| Placenta previa | 623 (3.4) | 21 (5.7) | 14 (5.2) | 4 (1.8) | 41 (4.0) | .033 |
| Placental abruption | 168 (0.9) | 3 (0.8) | 9 (3.3) | 0 (0.0) | 15 (1.5) | <.001 |
| Abnormal FHR pattern | 5029 (27.4) | 111 (29.8) | 82 (30.4) | 71 (32.4) | 299 (29.2) | .202 |
| PROM | 1129 (6.2) | 24 (6.5) | 22 (8.2) | 9 (4.1) | 66 (6.4) | .463 |
| Preterm birth (PTB) | 2158 (11.8) | 29 (7.8) | 28 (10.4) | 21 (9.6) | 130 (12.7) | .018 |
| Spontaneous PTB | 671 (3.7) | 11 (3.0) | 12 (4.4) | 6 (2.7) | 43 (4.2) | .484 |
| Medically indicated PTB | 1487 (8.1) | 18 (4.8) | 16 (5.9) | 15 (6.9) | 87 (8.5) | .133 |
| Chorioamnionitis | 766 (4.2) | 6 (1.6) | 4 (1.5) | 4 (1.8) | 32 (3.1) | .003 |
| Cesarean delivery | 9341 (51.0) | 142 (38.2) | 101 (37.4) | 93 (42.5) | 447 (43.6) | <.001 |
| Postpartum hemorrhage c | 254 (1.4) | 7 (1.9) | 6 (2.2) | 1 (4.6) | 30 (2.9) | <.001 |
| Surgical site infection | 229 (1.3) | 2 (0.5) | 1 (0.4) | 1 (0.5) | 10 (1.0) | .312 |
| Small for gestational age neonate | 1,520 (8.3) | 70 (18.8) | 45 (16.7) | 31 (14.2) | 167 (16.3) | <.001 |
| Large for gestational age neonate | 3326 (18.2) | 15 (4.0) | 15 (5.6) | 11 (5.0) | 68 (6.6) | <.001 |
| Macrosomia | 2944 (16.1) | 13 (3.5) | 17 (6.3) | 13 (5.9) | 57 (5.6) | <.001 |
| Stillbirth | 126 (0.7) | 3 (0.8) | 4 (1.5) | 0 (0.0) | 10 (1.0) | .280 |
| Apgar score <7 at 5 min | 245 (1.3) | 7 (1.9) | 5 (1.9) | 5 (2.3) | 18 (1.8) | .184 |
| NICU admission | 3067 (16.7) | 36 (9.7) | 35 (13.0) | 30 (13.7) | 135 (13.2) | <.001 |
| RDS | 1017 (5.6) | 13 (3.5) | 12 (4.4) | 7 (3.2) | 58 (5.7) | .212 |
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