Background
Gastroschisis is a severe congenital anomaly the etiology of which is unknown. Research evidence supports attempted vaginal delivery for pregnancies complicated by gastroschisis in the absence of obstetric indications for cesarean delivery.
Objective
The objectives of the study evaluating pregnancies complicated by gastroschisis were to determine the proportion of women undergoing planned cesarean vs attempted vaginal delivery and to provide up-to-date epidemiology on the risk factors associated with this anomaly.
Study Design
This population-based study of US natality records from 2005 through 2013 evaluated pregnancies complicated by gastroschisis. Women were classified based on whether they attempted vaginal delivery or underwent a planned cesarean (n = 24,836,777). Obstetrical, medical, and demographic characteristics were evaluated. Multivariable log-linear regression models were developed to determine the factors associated with the mode of delivery. Factors associated with the occurrence of the anomaly were also evaluated in log-linear models.
Results
Of 5985 pregnancies with gastroschisis, 63.5% (n = 3800) attempted vaginal delivery and 36.5% (n = 2185) underwent a planned cesarean delivery. The rate of attempted vaginal delivery increased from 59.7% in 2005 to 68.8% in 2013. Earlier gestational age and Hispanic ethnicity were associated with lower rates of attempted vaginal delivery. Factors associated with the occurrence of gastroschisis included young age, smoking, high educational attainment, and being married. Protective factors included chronic hypertension, black race, and obesity. The incidence of gastroschisis was 3.1 per 10,000 pregnancies and did not increase during the study period.
Conclusion
Attempted vaginal delivery is becoming increasingly prevalent for women with a pregnancy complicated by gastroschisis. Recommendations from the research literature findings may be diffusing into clinical practice. A significant proportion of women with this anomaly still deliver by planned cesarean, suggesting further reduction of surgical delivery for this anomaly is possible.
Gastroschisis is a severe congenital anomaly that involves a full-thickness defect of the abdominal wall through which intestines and other organs may herniate. The defect typically occurs on the right side of normal umbilical cord insertion, and in the majority of cases can be detected by midtrimester ultrasound. Although the risk factors for gastroschisis are well documented and include young maternal age, smoking, and infection, the etiology is unknown.
Hypotheses for the cause of gastroschisis include a failure of mesoderm formation in the body wall, rupture of amnion around the umbilical ring, and sequelae from involution of the right umbilical vein or disruption of the right vitelline artery. The defect requires major neonatal surgical intervention and is associated with significant health care costs, neonatal morbidity, and perinatal mortality.
Routine obstetric management of gastroschisis includes increased fetal surveillance, given the higher risk for associated adverse obstetrical outcomes including fetal growth restriction and stillbirth. Although optimal delivery timing is unclear, early-term delivery may be indicated to reduce the risk for bowel complications and perinatal death.
An intervention that has not been shown to be beneficial is cesarean delivery. Data from earlier reports and a metaanalysis demonstrated no benefit for cesarean delivery; these findings are similar to those from later studies. Given the increased maternal morbidity with cesarean delivery, and lack of neonatal benefit, planned cesarean delivery specifically for gastroschisis is not recommended.
Given the evidence that cesarean delivery be reserved for obstetric indications, this analysis had 2 objectives: (1) to assess trends in planned vaginal delivery for pregnancies complicated by gastroschisis and (2) to provide up-to-date epidemiological information on demographic, medical, and obstetric risk factors for this anomaly.
Materials and Methods
The primary outcome of this population-based analysis was to determine whether women with pregnancies complicated by gastroschisis underwent planned cesarean delivery or attempted vaginal birth. The study utilized US vital statistics data based on the 2003 revision of the live birth certificates, and the analysis was restricted to women who had live births from 2005 through 2013.
Compared with the 1989 version, the 2003 birth certificate revision contains more detailed obstetric, medical, and demographic data. The updated format was incorporated gradually on a statewide basis. States using the revised format numbered 12 in 2005, 21 in 2006, 23 in 2007, 28 in 2009 (66% of all births), 33 in 2010 (76% of all births), 36 in 2011 (83% of all births), 38 in 2012 (86% of all births), and 41 in 2013 (90% of all births). The number of births available in this format increases annually, given this uptake. Fetal demises were excluded because maternal data for these pregnancies are limited.
The data set is provided by the National Vital Statistics System, a joint effort of the National Center for Health Statistics and states to provide access to statistical information from birth certificates. Birth certificates are required to be completed for all births, and federal law mandates national collection and publication of birth statistics. Prior analyses have addressed the validity of these data. Because US vital statistics data are both publically available and deidentified, this analysis was exempt from institutional review board approval.
Patients with potential indications for planned cesarean delivery other than gastroschisis were excluded from the primary analysis. Exclusion criteria included the following: (1) noncephalic presentation, (2) multiple gestation, (3) prior cesarean delivery, and (4) eclampsia. Only women who delivered between 28 and 41 weeks’ gestation were included in the primary analysis. Births from 2004 were excluded, given that a relatively small proportion of national births are represented in the 2003-revised birth certificate for this year.
Women were considered to have undergone an attempted vaginal delivery if they met 1 of the following criteria: (1) they underwent labor induction or augmentation; (2) they had a successful spontaneous, forceps, or vaginal delivery; or (3) they had a cesarean delivery in the setting of prolonged labor and/or fetal intolerance of labor. Patients were classified as undergoing planned cesarean delivery if they had a cesarean delivery without induction or augmentation of labor or a diagnosis of fetal intolerance or prolonged labor.
Demographic, obstetrical, and medical factors possibly associated with attempted mode of delivery and available in the revised birth certificate format were chosen for inclusion in this analysis. Patient demographics included age (<20, 20–24, 25–29, 30–34, and ≥35 years); race/ethnicity (non-Hispanic white, non-Hispanic black, non-Hispanic other, and Hispanic); highest level of education (<ninth grade through professional degree); marital status (married or unmarried); and year of delivery.
Obstetrical factors included trimester of presentation to prenatal care and gestational age at delivery. The association between attempted mode of delivery and maternal clinical and demographic variables were compared using the χ 2 test. To account for the effect of clinical, obstetric, and demographic factors on the probability of planned mode of delivery, we developed log linear regression models including factors that were clinically important and/or statistically significant on univariable analysis. Results are reported as a risk ratio with a 95% confidence interval.
As a secondary analysis, we evaluated the risk factors associated with the diagnosis of gastroschisis to provide an up-to-date analysis on the epidemiology of this anomaly. We compared pregnancies with and without gastroschisis and analyzed maternal obstetric, medical, and demographic factors. For this analysis the only inclusion criteria were live births between 2005 and 2013 and gestational age between 24 and <42 weeks. Data on insurance status, body mass index (kilograms per square meter), and sexually transmitted infections were included in this analysis but are available only for the years 2011 through 2013.
We used χ 2 tests to compare the relationship between risk factors for gastroschisis and the outcome and included statistically significant characteristics in an adjusted log linear regression model. A sensitivity analysis of the log linear model restricted to the years 2011–2013 to include the additional covariates available only during those years was performed. Additionally, the proportion of deliveries occurring from 34 to 42 weeks that are late preterm, early term, and full term are described by year.
A sensitivity analysis of births from 2009 through 2013 evaluating the rate of attempted labor including only those states that utilized the revised birth certificate as of 2009 was performed; given that there was a gradual uptake of states using the revised birth certificate on an annual basis, this sensitivity analysis controls for the potential bias of the shifting sampling frame. Additionally, to assess the validity of our classification of attempted vaginal delivery, we repeated the sensitivity analysis using a separate variable indicating trial of labor and excluding diagnoses of fetal intolerance of labor and long labor, given concerns related to the quality of these latter diagnoses. Finally, we assessed temporal trends in the diagnosis of gastroschisis in the restricted cohorts of states using the revised birth certificate as of 2009 to similarly account for the changing sampling frame. All analyses were performed using SAS version 9.4 (SAS Institute, Cary, NC).
Results
For the primary analysis evaluating factors associated with planned cesarean delivery vs attempted vaginal delivery, a total of 5985 pregnancies between 2005 and 2013 had a diagnosis of gastroschisis, met inclusion criteria, and were included. Of this cohort, 63.5% (3800 pregnancies) had an attempted vaginal delivery and 36.5% (2185) underwent a planned cesarean delivery. The rate of attempted vaginal delivery increased from 59.7% in 2005 to 68.8% in 2013 ( P < .001).
In addition to the year of delivery, other factors significantly associated with the type of delivery included race and parity; Hispanic women were less likely (58.8%) and parous women more likely (68.8%) to attempt vaginal delivery than non-Hispanic white (64.7%) and nulliparous women, respectively (60.8).
Earlier gestational age at delivery was associated with a lower probability of attempted vaginal delivery with women ≥28 to <32 weeks attempting vaginal delivery in 52.9% of cases ( Table 1 ). Other significant factors included gestational age at prenatal care entry. In the adjusted log linear model, the following factors retained significance: (1) the final years of the study (2011–2013) were associated with anincreased probability of vaginal delivery relative to 2005; (2) multiparity was associated with an increased probability of attempted vaginal delivery compared with nulliparity; (3) Hispanic ethnicity and earlier gestational age at delivery were associated with a decreased probability of attempted vaginal delivery compared with non-Hispanic white race and later gestational age, respectively.
| Attempted vaginal delivery, %, n | Univariate analysis | Multivariable log linear model | ||
|---|---|---|---|---|
| P value | Adjusted risk ratio | 95% confidence interval | ||
| All patients | 63.5 (3800) | |||
| Live-born parity | < .001 | |||
| Nulliparous | 60.8 (2419) | 1.00 | Referent | |
| Parous | 68.8 (1358) | 1.14 | (1.09–1.19) | |
| Unknown | 65.7 (23) | 1.05 | (0.82–1.34) | |
| Maternal age, y | .021 | |||
| <20 | 60.6 (1163) | 1.02 | (0.95–1.09) | |
| 20–24 | 65.0 (1736) | 1.04 | (0.98–1.10) | |
| 25–29 | 65.2 (632) | 1.00 | Referent | |
| 30–34 | 63.9 (200) | 0.97 | (0.88–1.07) | |
| >34 | 60.5 (69) | 0.91 | (0.78–1.06) | |
| Gestational age, wks | < .001 | |||
| ≥28 to <32 | 52.9 (146) | 1.00 | Referent | |
| ≥32 to <36 | 59.9 (1152) | 1.15 | (1.02–1.29) | |
| ≥36 to <39 | 66.2 (1990) | 1.27 | (1.14–1.43) | |
| ≥39 to <42 | 65.7 (512) | 1.26 | (1.11–1.42) | |
| Highest level of education | .941 | |||
| Less than ninth grade | 62.2 (120) | 1.00 | Referent | |
| Ninth grade to 12 grade | 62.4 (961) | 1.01 | (0.89–1.13) | |
| High school graduate | 63.4 (1340) | 0.99 | (0.89–1.12) | |
| Some college credit | 63.8 (894) | 1.00 | (0.88–1.12) | |
| Associate degree | 65.8 (179) | 1.03 | (0.89–1.18) | |
| BS degree | 64.9 (211) | 1.05 | (0.91–1.21) | |
| MS degree | 64.8 (46) | 1.07 | (0.87–1.32) | |
| Doctorate/professional | 71.4 (10) | 1.13 | (0.81–1.59) | |
| Unknown | 68.4 (39) | 0.96 | (0.77–1.20) | |
| Year | < .001 | |||
| 2005 | 59.7 (188) | 1.00 | Referent | |
| 2006 | 57.0 (274) | 0.96 | (0.85–1.08) | |
| 2007 | 57.4 (322) | 0.98 | (0.87–1.10) | |
| 2008 | 63.4 (426) | 1.07 | (0.96–1.20) | |
| 2009 | 60.6 (425) | 1.03 | (0.92–1.14) | |
| 2010 | 63.4 (471) | 1.06 | (0.96–1.18) | |
| 2011 | 65.9 (563) | 1.11 | (1.00–1.23) | |
| 2012 | 67.5 (570) | 1.14 | (1.03–1.26) | |
| 2013 | 68.8 (561) | 1.16 | (1.04–1.28) | |
| Marital status | .452 | |||
| Married | 64.2 (1099) | 1.00 | Referent | |
| Unmarried | 63.2 (2701) | 1.01 | (0.96–1.06) | |
| Race | < .001 | |||
| Non-Hispanic white | 64.7 (2361) | 1.00 | Referent | |
| Non-Hispanic black | 64.6 (369) | 0.97 | (0.91–1.04) | |
| Non-Hispanic other | 67.5 (158) | 1.03 | (0.93–1.13) | |
| Hispanic | 58.8 (875) | 0.91 | (0.87–0.96) | |
| Unknown | 82.2 (37) | 1.27 | (1.09–1.48) | |
| Prenatal care entry | .001 | |||
| First to third month | 61.5 (2082) | 1.00 | Referent | |
| Fourth to sixth month | 64.9 (1030) | 1.06 | (1.01–1.11) | |
| Seventh to final month | 69.4 (263) | 1.12 | (1.05–1.21) | |
| No care | 71.7 (99) | 1.18 | (1.05–1.32) | |
| Unknown | 66.1 (326) | 1.10 | (1.03–1.18) | |
| Preexisting diabetes | .374 | |||
| Present | 50.0 (6) | 0.78 | (0.44–1.37) | |
| Absent | 63.5 (3794) | 1.00 | Referent | |
| Chronic hypertension | .154 | |||
| Present | 76.9 (20) | 1.27 | (1.03–1.57) | |
| Absent | 63.4 (3780) | 1.00 | Referent | |
| Gestational diabetes | .650 | |||
| Present | 54.0 (47) | 0.84 | (0.69–1.02) | |
| Absent | 63.6 (3753) | 1.00 | Referent | |
| Gestational hypertension | .959 | |||
| Present | 63.7 (79) | 1.04 | (0.92–1.19) | |
| Absent | 62.2 (3721) | 1.00 | Referent | |
For the epidemiologic analysis of factors associated with gastroschisis, 7683 pregnancies with the anomaly and 24,829,094 pregnancies without the anomaly were included. The overall incidence was 3.1 cases per 10,000 pregnancies and ranged from 2.9 to 3.2 during the study period. The univariable comparison is demonstrated in Table 2 . In this cohort gastroschisis occurred primarily among young women; 74.0% of cases were diagnosed in women younger than 25 years.
| Gastroschisis incidence | Gastroschisis | No gastroschisis | |||
|---|---|---|---|---|---|
| Per 10,000 | % | n | % | n | |
| All patients | 3.1 | 7683 | 24,829,094 | ||
| Parity | |||||
| Nulliparous | 4.9 | 62.5 | 4798 | 39.8 | 9,875,617 |
| Parous | 1.9 | 36.9 | 2830 | 59.6 | 14,801517 |
| Unknown | 3.6 | 0.7 | 55 | 0.6 | 151,960 |
| Age, y | |||||
| <20 | 10.2 | 30.4 | 2336 | 9.24 | 2,291,664 |
| 20–24 | 5.6 | 43.6 | 3348 | 24.1 | 5,985,336 |
| 25–29 | 1.9 | 17.3 | 1327 | 28.2 | 7,004,452 |
| 30–34 | 0.8 | 6.1 | 472 | 23.9 | 5,943,870 |
| >34 | 0.6 | 2.6 | 200 | 14.5 | 3,603,772 |
| Highest level of education | |||||
| Less than ninth grade | 2.0 | 3.3 | 255 | 5.1 | 1,267,877 |
| Ninth grade to 12th grade | 5.3 | 25.3 | 1941 | 14.7 | 3,657,185 |
| High school graduate | 4.3 | 35.4 | 2722 | 25.4 | 6,303,068 |
| Some college credit | 3.5 | 22.7 | 1744 | 20.1 | 4,989,457 |
| Associate degree | 2.0 | 4.7 | 361 | 7.2 | 1,781,608 |
| BS degree | 1.0 | 5.7 | 442 | 17.2 | 4,276,058 |
| MS degree | 0.6 | 1.4 | 107 | 7.1 | 1,757,605 |
| Doctorate/professional | 0.4 | 0.3 | 20 | 2.0 | 493,825 |
| Unknown | 3.0 | 1.2 | 91 | 1.2 | 302,411 |
| Year | |||||
| 2005 | 3.2 | 5.3 | 404 | 5.1 | 1,274,557 |
| 2006 | 2.9 | 7.8 | 598 | 8.4 | 2,082,629 |
| 2007 | 3.1 | 9.5 | 729 | 9.6 | 2,381,081 |
| 2008 | 3.1 | 11.2 | 859 | 11.0 | 2,743,047 |
| 2009 | 3.2 | 11.8 | 900 | 11.3 | 2,800,219 |
| 2010 | 3.0 | 12.3 | 943 | 12.4 | 3,091,522 |
| 2011 | 3.2 | 14.1 | 1084 | 13.6 | 3,388,437 |
| 2012 | 3.2 | 14.5 | 1116 | 14.1 | 3,500,152 |
| 2013 | 2.9 | 13.7 | 1050 | 14.4 | 3,567,450 |
| Marital status | |||||
| Married | 1.6 | 29.9 | 2300 | 59.7 | 14,822,523 |
| Unmarried | 5.4 | 70.1 | 5383 | 40.3 | 10,006,571 |
| Race | |||||
| Non-Hispanic white | 3.5 | 59.9 | 4604 | 52.6 | 13,060,137 |
| Non-Hispanic black | 2.4 | 10.4 | 799 | 13.6 | 3,374,368 |
| Non-Hispanic other | 1.8 | 3.9 | 296 | 6.5 | 1,620,916 |
| Hispanic | 2.9 | 25.0 | 1924 | 26.5 | 6,578,384 |
| Unknown | 3.1 | 0.8 | 60 | 0.8 | 195,289 |
| Prenatal care presentation | |||||
| 1 st to 3 rd month | 2.5 | 55.3 | 4251 | 67.8 | 16,845,517 |
| 4 th to 6 th month | 4.2 | 26.6 | 2042 | 19.6 | 4,856,012 |
| 7 th to final month | 4.4 | 6.4 | 492 | 14.5 | 1,121,167 |
| No care | 5.6 | 3.0 | 227 | 1.6 | 407,948 |
| Unknown | 4.2 | 8.7 | 671 | 6.4 | 1,598,450 |
| Multiple gestation | |||||
| Singleton | 3.1 | 97.8 | 7512 | 96.6 | 23,979,384 |
| Twin | 2.0 | 2.1 | 166 | 3.3 | 813,852 |
| Triplet or higher | 1.4 | 0.1 | 5 | 0.1 | 35,858 |
| Pregestational diabetes | |||||
| Present | 1.5 | 0.4 | 27 | 0.7 | 175,310 |
| Absent | 3.1 | 99.2 | 7623 | 99.1 | 24,610,950 |
| Unknown | 7.7 | 0.4 | 33 | 0.2 | 42,834 |
| Chronic hypertension | |||||
| Present | 1.2 | 0.5 | 39 | 1.3 | 317,207 |
| Absent | 3.1 | 99.1 | 7611 | 98.6 | 24,469,053 |
| Unknown | 7.7 | 0.4 | 33 | 0.2 | 42,834 |
| Smoking | |||||
| Present | 7.4 | 19.7 | 1516 | 8.3 | 2,052,424 |
| Absent | 2.7 | 67.4 | 5179 | 78.1 | 19,399,146 |
| Unknown | 2.9 | 12.9 | 988 | 13.6 | 3,377,524 |
| Body mass index (kg/m 2 ) a | |||||
| Underweight (<18.5) | 5.9 | 7.0 | 228 | 3.7 | 387,105 |
| Normal (18.5–24.9) | 3.9 | 57.0 | 1854 | 44.9 | 4,695,030 |
| Overweight (25.0–29.9) | 2.6 | 20.2 | 655 | 24.4 | 2,547,371 |
| Obesity (30.0–34.9) | 1.8 | 7.4 | 241 | 12.7 | 1,331,599 |
| Obesity (35.0–39.9) | 1.4 | 2.7 | 88 | 6.0 | 624,758 |
| Obesity (≥ 40) | 0.9 | 1.2 | 40 | 4.1 | 426,308 |
| Unknown | 3.2 | 4.4 | 144 | 4.3 | 443,868 |
| Chlamydia during pregnancy a | |||||
| Present | 3.0 | 95.6 | 3109 | 97.9 | 10,252,322 |
| Absent | 6.8 | 4.4 | 141 | 2.9 | 206,833 |
| Insurance status a | |||||
| Medicaid | 4.5 | 62.1 | 2017 | 43.1 | 4,502,049 |
| Private | 1.9 | 28.2 | 918 | 46.4 | 4,855,913 |
| Self-pay | 1.8 | 2.5 | 80 | 4.2 | 442,258 |
| Other | 3.6 | 5.7 | 185 | 4.9 | 513,040 |
| Unknown | 3.5 | 1.5 | 50 | 1.4 | 142,779 |
a Only 2011–2013 data are available. All comparisons were statistically significant with P < .001.
The risk ratio in the adjusted model for age <20 years was 3.46 (95% confidence interval, 3.19–3.75) ( Table 3 ) compared with women aged 25–29 years. Other factors associated with gastroschisis in the adjusted model included smoking (risk ratio, 1.61, 95% confidence interval, 1.51–1.72) and being unmarried (risk ratio, 1.67, 95% confidence interval, 1.57–1.77). High school graduation as highest educational attainment was significantly associated with gastroschisis (risk ratio, 1.40, 95% confidence interval, 1.23–1.59) with less than a ninth grade education as the referent; ninth to 12th grade education, some college, and an associate degree were also associated with increased risk for gastroschisis, whereas a master’s degree or doctorate/professional degree were associated with a decreased risk.
| 2005–2013 model | 2011–2013 model | |||
|---|---|---|---|---|
| Risk ratio | 95% confidence interval | Risk ratio | 95% confidence interval | |
| Parity | ||||
| Nulliparous | 1.00 | Referent | 1.00 | Referent |
| Parous | 0.69 | (0.65–0.72) | 0.71 | (0.65–0.76) |
| Unknown | 1.08 | (0.83–1.41) | 1.23 | (0.80–1.87) |
| Age, y | ||||
| <20 | 3.46 | 3.19–3.75 | 2.86 | (2.52–3.24) |
| 20–24 | 2.23 | 2.08–2.39 | 2.07 | (1.87–2.29) |
| 25–29 | 1.00 | Referent | 1.00 | Referent |
| 30–34 | 0.51 | 0.46–0.57 | 0.53 | (0.46–0.62) |
| >34 | 0.38 | 0.33–0.44 | 0.41 | (0.33–0.51) |
| Highest level of education | ||||
| Less than ninth grade | 1.00 | Referent | 1.00 | Referent |
| Ninth grade to 12th grade | 1.34 | (1.17–1.53) | 1.68 | (1.31–2.17) |
| High school graduate | 1.40 | (1.23–1.59) | 1.79 | (1.39–2.29) |
| Some college credit | 1.44 | (1.26–1.65) | 1.81 | (1.40–2.33) |
| Associate degree | 1.28 | (1.08–1.50) | 1.59 | (1.19–2.13) |
| BS degree | 0.92 | (0.78–1.08) | 1.10 | (0.82–1.47) |
| MS degree | 0.69 | (0.55–0.87) | 0.92 | (0.64–1.32) |
| Doctorate/professional | 0.51 | (0.32–0.82) | 0.46 | (0.22–0.97) |
| Year | ||||
| 2005 | 1.00 | Referent | ||
| 2006 | 0.93 | (0.82–1.06) | ||
| 2007 | 0.98 | (0.87–1.11) | ||
| 2008 | 1.02 | (0.90–1.15) | ||
| 2009 | 1.06 | (0.94–1.19) | ||
| 2010 | 1.03 | (0.92–1.16) | ||
| 2011 | 1.12 | (1.00–1.25) | 1.00 | Referent |
| 2012 | 1.14 | (1.02–1.28) | 1.02 | (0.94–1.11) |
| 2013 | 1.09 | (0.97–1.22) | 0.97 | (0.90–1.06) |
| Marital status | ||||
| Married | 1.00 | Referent | ||
| Unmarried | 1.67 | (1.57–1.77) | ||
| Race | ||||
| Non-Hispanic white | 1.00 | Referent | 1.00 | Referent |
| Non-Hispanic black | 0.44 | (0.41–0.48) | 0.49 | (0.44–0.55) |
| Non-Hispanic other | 0.81 | (0.72–0.91) | 0.80 | (0.67–0.95) |
| Hispanic | 0.69 | (0.64–0.73) | 0.71 | (0.64–0.78) |
| Multiple gestation | ||||
| Singleton | 1.00 | Referent | 1.00 | Referent |
| Multiple gestation | 1.01 | (0.86–1.17) | 0.95 | (0.75–1.21) |
| Pregestational diabetes | ||||
| Present | 0.73 | (0.50–1.07) | 1.17 | (0.72–1.89) |
| Absent | 1.00 | Referent | 1.00 | Referent |
| Unknown | 2.20 | (1.56–3.10) | 1.20 | (0.57–2.53) |
| Chronic hypertension | ||||
| Present | 0.61 | (0.44–0.84) | 0.99 | (0.66–1.48) |
| Absent | 1.00 | Referent | 1.00 | Referent |
| Smoking | ||||
| Present | 1.61 | (1.51–1.72) | 1.70 | (1.54–1.87) |
| Absent | 1.00 | Referent | 1.00 | Referent |
| Unknown | 1.05 | (0.98–1.13) | 0.97 | (0.83–1.13) |
| Body mass index, kg/m 2 a | ||||
| Underweight (<18.5) | N/A | N/A | 1.04 | (0.91–1.20) |
| Normal (18.5–24.9) | 1.00 | Referent | ||
| Overweight (25.0–29.9) | 0.70 | (0.65–0.77) | ||
| Obesity (30.0–34.9) | 0.49 | (0.43–0.56) | ||
| Obesity (35.0–39.9) | 0.38 | (0.31–0.47) | ||
| Obesity (≥40) | 0.26 | (0.19–0.36) | ||
| Unknown | 0.93 | (0.79–1.11) | ||
| Chlamydia during pregnancy a | ||||
| Present | N/A | N/A | 1.00 | Referent |
| Absent | 1.17 | (0.99–1.39) | ||
| Insurance status a | ||||
| Medicaid | 1.09 | (1.00–1.20) | ||
| Private | N/A | N/A | 1.00 | Referent |
| Self-pay | 0.73 | (0.58–0.93) | ||
| Other | 1.17 | (0.99–1.38) | ||
| Unknown | 1.13 | (0.85–1.52) | ||
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