Elucidating the role of overweight and obesity in racial and ethnic disparities in cesarean delivery risk

Annals of Epidemiology xxx (xxxx) xxx

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Annals of Epidemiology

Original article

Elucidating the role of overweight and obesity in racial and ethnic disparities in cesarean delivery risk Kimberly B. Glazer, PhD, MPH a, b, *, Valery A. Danilack, PhD, MPH a, c, d, Erika F. Werner, MD, MS a, d, e, Alison E. Field, ScD a, David A. Savitz, PhD a, d a

Department of Population Health Science and Policy and the Blavatnik Family Women's Health Research Institute, Icahn School of Medicine at Mount Sinai, New York, NY Department of Epidemiology, Brown University School of Public Health, Providence, RI c Division of Research, Women & Infants Hospital, Providence, RI d Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Providence, RI e Department of Obstetrics and Gynecology, Women & Infants Hospital, Providence, RI b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 12 March 2019 Accepted 30 December 2019 Available online xxx

Purpose: We aimed to quantify the extent to which overweight and obesity explain cesarean delivery risk among women of different racial and ethnic backgrounds. Methods: Using administrative records for 216,481 singleton, nulliparous births in New York City from 2008 to 2013, we calculated risk ratios, risk differences, and population attributable fractions for associations between body mass index (BMI) and cesarean, stratified by race and ethnicity. Results: The population attributable fraction (95% confidence interval) for BMI was 6.8% (6.2%e7.3%) among Asian, 10.9% (10.4%e11.4%) among White, 14.6% (13.7%e15.5%) among Hispanic, and 17.4% (16.2% e18.6%) among Black women. Although overweight and obesity were most prevalent among Black and Hispanic women, the risk gradient was strongest among Whites (adjusted risk ratio [95% CI] from 1.37 [1.33e1.41] for overweight to 2.23 [2.07e2.39] for class III obesity). Additional adjustment for gestational complications partially attenuated associations, and accounting for delivery hospital eliminated the stronger gradient among White women. Conclusions: Prepregnancy overweight and obesity contribute proportionally more to cesarean risk among Black and Hispanic women because of higher prevalence compared to White or Asian women. Although preconception weight management is important to decrease cesarean risk, results encourage attention to clinical approaches in low-risk pregnancies to mitigate racial and ethnic perinatal disparities. © 2020 Elsevier Inc. All rights reserved.

Keywords: Cesarean delivery Race Ethnicity Obesity BMI Obstetrics Maternal health

Introduction Racial disparities in adverse perinatal outcomes are well documented [1e3]. Mode of delivery, specifically, varies by race and ethnicity, with studies in the United States consistently showing that cesarean delivery risk is highest among non-Hispanic Black women [2,4e14]. Evidence comparing other minority populations to non-Hispanic White women is mixed, with some studies suggesting higher risk among Hispanic [6,10,13,14] and Asian [6,15] women, others showing lower risk or no difference in risk [5,10,11,14], and some evidence that racial variation in risk depends

* Corresponding author. Icahn School of Medicine at Mount Sinai, 1 Gustave L. Levy Place, Box 1077, New York, NY 10029. Tel.: þ1-212-468-2189; fax: þ1-212468-2199. E-mail address: [email protected] (K.B. Glazer).

on indication for cesarean [12]. Cesarean delivery is a life-saving intervention that should be available to all women when medically necessary [16,17]. However, it is a surgical procedure with increased resource requirements and significant risks in terms of postpartum morbidities, complications in subsequent pregnancies, and repeat cesarean delivery [18]. Limiting primary cesarean deliveries is, therefore, an important public health goal. Maternal body mass index (BMI) likely contributes to differences in cesarean risk across racial and ethnic groups, given the robust doseeresponse association between BMI, pregnancy complications, and cesarean delivery [19] and the disproportionate prevalence of overweight and obesity among Black and Hispanic women [20]. Further, the infrastructure, managerial practices, and policies at hospitals serving different racial and ethnic patient populations may affect labor and delivery practices for maternal risk factors such as obesity [21]. There is also evidence that clinicians may excessively problematize pregnancies among women of

https://doi.org/10.1016/j.annepidem.2019.12.012 1047-2797/© 2020 Elsevier Inc. All rights reserved.

Please cite this article as: Glazer KB et al., Elucidating the role of overweight and obesity in racial and ethnic disparities in cesarean delivery risk, Annals of Epidemiology, https://doi.org/10.1016/j.annepidem.2019.12.012

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color [22], motivating unnecessary obstetric intervention [23]. Researchers have called for investigations into the extent to which obesity influences obstetric risk assessment, clinical management, and the possible overmedicalization of labor and delivery [24,21]. Finally, studies suggest that the pathophysiological consequences of elevated BMI may differ by race and ethnicity [25,26], which may result in a varying impact of excess weight on cesarean delivery risk. The contribution of prepregnancy overweight and obesity to cesarean risk by race and ethnicity has not been carefully quantified in studies to date. Maternal BMI was not included in many prior explanatory models [9,11,13,14,23] or was not isolated from the influence of other covariates [7,10,12]. An exposure may influence a health disparity because of a differential effect by subgroup (interaction effect), differential distribution by subgroup, or both. However, most studies have examined statistical interaction to describe disparities and overlooked how meaningful differences in exposure prevalence and effect size may explain subgroup patterns [27]. To address these gaps, we quantified the extent to which overweight and obesity explain cesarean risk among women of different racial and ethnic backgrounds. We examined absolute, relative, and attributable risk measures to tease apart differences in (1) baseline risk of cesarean by race and ethnicity, (2) overweight and obesity prevalence, and (3) the strength of the BMIecesarean association. We additionally assessed associations in terms of specific labor and delivery trajectories defined by the presence of spontaneous labor, use of labor induction, and prelabor cesarean to identify focal points for clinical research and intervention. We hypothesized that population attributable risk would be highest among Black and Hispanic women because of both higher prevalence in these racial and ethnic groups and a stronger relative association between BMI and cesarean risk among women of color than among White women.

Materials and methods Study population Birth records on 734,454 live births in New York City (NYC) hospitals from 2008 to 2013, provided by the NYC Department of Health and Mental Hygiene, were linked through maternal medical record number to delivery hospitalization discharge data provided by the New York State Department of Health Statewide Planning and Research Cooperative System. All records from 2010 (n ¼ 122,370) were excluded because of an administrative linkage error. Births were excluded from other years if they did not link to a maternal discharge record (n ¼ 21,107) or were missing all discharge data (n ¼ 1955), resulting in a sample of 586,632 births. We further restricted the study to the 45% (n ¼ 263,412) of remaining deliveries that were to nulliparous women. We excluded births with multifetal gestation, nonvertex presentation, fewer than 34 weeks' gestation or missing or invalid (>44 weeks) gestational ages, congenital anomalies, and placental abruption or placenta previa to exclude major maternal or fetal complications that may preclude vaginal delivery (n ¼ 24,419). The following exclusions were then applied sequentially: women missing height or prepregnancy weight or reported height less than or equal to 48 or greater than or equal to 78 inches or weight greater than 500 pounds (n ¼ 2095); underweight women (BMI <18.5 kg/m2; n ¼ 16,513); race and ethnicity reported as “other” (including American Indian, Alaska Native, or unspecified race), “unknown,” or “more than one race” (n ¼ 3800), given potential heterogeneity within categories; and home births (n ¼ 104). After the previously mentioned restrictions, our study population included 216,481

births. The study protocol was approved by the Institutional Review Boards of the NYC and State health departments. Prepregnancy BMI Maternal height and prepregnancy weight were ascertained from birth certificates. BMI (weight in kilograms/square of height in meters) was categorized as normal (18.5 kg/m2  BMI < 25 kg/m2), overweight (25 kg/m2  BMI < 30 kg/m2), class I/II obesity (30 kg/m2  BMI < 40 kg/m2), and class III obesity (BMI  40 kg/m2). Race and ethnicity We considered categories of self-identified race and ethnicity from the birth certificate: non-Hispanic White (referred to throughout as White), non-Hispanic Black or African American (Black), Hispanic, and non-Hispanic Asian (Asian). In sensitivity analyses, we disaggregated Asian Indian, East Asian, and Southeast Asian descent because of notable differences in obesity and gestational diabetes prevalence and associations between BMI and adverse cardiovascular and metabolic outcomes that may influence the mode of delivery [2,7,28]. Mode of delivery We dichotomized the mode of delivery into cesarean or vaginal birth. We used International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9), procedure codes from discharge data to identify cesarean delivery (74.0, 74.1, 74.2, 74.4, and 74.99). Labor induction was identified through procedure (73.1, 73.01, and 73.4) and diagnosis (659.10, 659.11, and 659.13) codes. As combining birth certificate and discharge data improves sensitivity of labor induction classification with only slight increases in false positive rates [29], we assigned additional inductions when medical or surgical induction was reported on the birth certificate. We considered subsets of cesarean pathways: prelabor cesarean, cesarean among women who experienced spontaneous labor, and cesarean among women who underwent labor induction. We applied a previously developed algorithm to identify spontaneous labor and prelabor cesarean deliveries [30,31]. Spontaneous labor was identified if (1) the birth certificate or delivery record did not contain codes indicative of labor induction or cesarean delivery or (2) the delivery record indicated cesarean birth but also included ICD codes indicative of active (but not induced) labor (Supplementary Material, Table S1). Cesarean deliveries without codes indicating spontaneous or induced active labor were classified as prelabor cesarean deliveries. Covariates Covariates included maternal age (years), educational attainment (<12 years and 12 years), insurance status (no insurance/ self-pay, private insurance, and public insurance/other), year of delivery, hospital ownership (public and private), delivery attendant (physician and certified nurse midwife/other), gestational weight gain, diabetes (pre-existing and gestational), hypertensive disorders (pre-existing or gestational hypertension and preeclampsia), large for gestational age (birth weight >90th percentile for gestational age and sex), and small for gestational age (birth weight <10th percentile for gestational age and sex). Covariate data were extracted from birth certificates; diabetes and hypertension were identified from birth certificates and discharge data (Table S1). We calculated gestational weight gain by subtracting prepregnancy weight from weight at the delivery admission as reported on the birth certificate. We categorized weight gain as

Please cite this article as: Glazer KB et al., Elucidating the role of overweight and obesity in racial and ethnic disparities in cesarean delivery risk, Annals of Epidemiology, https://doi.org/10.1016/j.annepidem.2019.12.012

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modified Poisson regression with robust error variance [33]. A product term for BMI and race/ethnicity was statistically significant and included in all models. We quantified the proportion of cesarean deliveries attributable to elevated BMI among overweight    and obese women using the attributable fraction AF ¼ aRR1 aRR

inadequate, adequate, or excessive using guidelines from the Institute of Medicine based on the maternal prepregnancy BMI (adequate weight gain [kilogram] ranges by BMI class: 11.5e16 [normal weight], 7e11.5 [overweight], 5e9 [obese]) [32]. Statistical analyses

and the proportion attributable to elevated BMI among all women    , using the population attributable fraction PAF ¼ pd aRR1 aRR

We examined cesarean prevalence overall and for the three delivery mode pathways by BMI category and race and ethnicity. We calculated risk differences and ratios for cesarean delivery comparing overweight and obesity to normal weight, using

stratifying by race and ethnicity and delivery pathways, where aRR is adjusted risk ratio comparing overweight and obesity to normal

Table 1 Sociodemographic, medical, and obstetric characteristics of nulliparous women delivering in New York City hospitals, 2008e2013, n ¼ 216,481 Variables

BMI Normal Overweight Obese class I/II Obese class III Mean Height (inches) Gestational weight gain, kg* Excessive Adequate Inadequate Mean (SD) Age (y) <20 20e24 25e29 30e34 35þ Mean (SD) Maternal education <12 y 12 y Marital status Married Not married Insurance coverage Private Publicy Otherz Delivery hospital Private Public Delivery attendant Physician Certified nurse midwife Other Gestational age at delivery, wk Late preterm (34 to <37) Early term (37 to <39) Term (39 to <41) Late term (41 to <42) Post-term (42þ) Mean (SD) Labor induction Diabetic disorders Preexisting diabetes Gestational diabetes Hypertensive disorders Preexisting hypertension Gestational hypertension Preeclampsia LGAx SGAk * y z x k

Mean ± SD or n (%) Non-Hispanic White (n ¼ 70,836)

Non-Hispanic Black (n ¼ 45,100)

Hispanic (n ¼ 64,980)

Asian (n ¼ 35,565)

53,699 (75.8) 11,843 (16.7) 4699 (6.6) 595 (0.8) 23.4 ± 4.2 64.7 ± 2.6

21,440 (47.5) 12,774 (28.3) 9127 (20.2) 1759 (3.9) 26.8 ± 6.1 64.7 ± 2.7

35,726 (55.0) 17,650 (27.2) 10,216 (15.7) 1388 (2.1) 25.7 ± 5.3 63.0 ± 2.9

29,131 (81.9) 5038 (14.2) 1339 (3.8) 57 (0.2) 22.5 ± 3.4 63.0 ± 2.3

28,623 (40.4) 22,448 (31.7) 19,765 (27.9) 14.6 ± 6.3

16,209 (35.9) 9846 (21.8) 19,045 (42.2) 13.4 ± 7.4

23,777 (36.6) 16,207 (24.9) 24,996 (38.5) 13.6 ± 6.9

12,261 (34.5) 12,277 (34.5) 11,027 (31.0) 13.6 ± 5.8

1767 (2.5) 10,936 (15.4) 14,803 (20.9) 25,936 (36.6) 13,340 (18.8) 30.5 ± 5.8

7320 (16.2) 15,206 (33.7) 11,324 (25.1) 7000 (15.5) 3282 (7.3) 25.5 ± 6.1

13,351 (20.6) 22,786 (35.1) 14,846 (22.9) 9059 (13.9) 3894 (6.0) 24.7 ± 6.0

585 (1.6) 6063 (17.1) 11,879 (33.4) 11,047 (31.1) 4861 (13.7) 29.4 ± 5.2

11,529 (16.3) 59,196 (83.7)

20,489 (45.6) 24,487 (54.4)

36,067 (55.6) 28,826 (44.4)

12,028 (33.9) 23,507 (66.2)

60,102 (84.9) 10,734 (15.2)

10,890 (24.2) 34,210 (75.9)

17,820 (27.4) 47,160 (72.6)

28,197 (79.3) 7368 (20.7)

53,141 (75.0) 16,692 (23.6) 1003 (1.4)

11,925 (26.4) 31,077 (68.9) 2098 (4.7)

14,777 (22.7) 48,564 (74.7) 1639 (2.5)

16,257 (45.7) 18,823 (52.9) 485 (1.4)

68,456 (96.6) 2380 (3.4)

33,137 (73.5) 11,963 (26.5)

48,467 (74.6) 16,513 (25.4)

32,282 (88.0) 4283 (12.0)

66,236 (93.5) 4505 (6.4) 95 (0.1)

40,796 (90.5) 4214 (9.3) 90 (0.2)

57,599 (88.6) 7228 (11.1) 153 (0.2)

34,117 (95.9) 1409 (4.0) 39 (0.1)

2599 (3.7) 13,270 (18.7) 45,288 (63.9) 8950 (12.6) 729 (1.0) 39.2 ± 1.3 25,869 (36.5)

2837 (6.3) 11,420 (25.3) 25,982 (57.6) 4613 (10.2) 248 (0.6) 38.9 ± 1.5 16,359 (36.3)

3416 (5.3) 14,864 (22.9) 39,244 (60.4) 7098 (10.9) 358 (0.6) 39.1 ± 1.4 24,558 (37.8)

1614 (4.5) 8858 (24.9) 21,900 (61.6) 2975 (8.4) 218 (0.6) 39.0 ± 1.3 13,292 (37.4)

358 (0.5) 3120 (4.4)

497 (1.1) 2576 (5.7)

527 (0.8) 3524 (5.4)

261 (0.7) 4259 (12.0)

950 2181 2424 4056 8075

1629 1867 3947 1789 8153

1326 2614 4271 3230 8818

460 727 1.066 1102 5745

(1.3) (3.2) (3.5) (5.7) (11.4)

(3.6) (4.7) (9.0) (4.0) (18.1)

(2.0) (4.4) (6.7) (5.0) (13.6)

(1.3) (2.1) (3.0) (3.1) (16.2)

Adequate weight gain (kilogram) ranges by BMI class per 2009 Institute of Medicine guidelines: 11.5e16 (normal weight), 7e11.5 (overweight), 5e9 (obese). Includes Medicaid, Family Health Plus, or other government insurance. Includes Champus/Tricare, other unspecified insurance, self-pay, or unknown coverage. Large for gestational age, birth weight above the 90th percentile for gestational age and sex based on 1999 and 2000 U.S. births. Small for gestational age, birth weight below the 10th percentile for gestational age and sex based on 1999 and 2000 U.S. births.

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weight and pd is the proportion of cesarean cases that were among women with overweight or obesity [34]; confidence intervals (CIs) were generated using the delta method for variance estimation [35]. Regression models were adjusted for sociodemographic and prepregnancy patient-level characteristics. We constructed an additional series of regression models to (1) examine incremental increases in cesarean risk using disaggregated BMI classes (normal weight, overweight, class I/II obesity, and class III obesity) and (2) evaluate associations between race and ethnicity and cesarean delivery within BMI categories to describe disparities independent of BMI. We applied different levels of adjustment for covariates that may confound or explain associations of interest. In the first model, we adjusted for sociodemographic and prepregnancy patient characteristics but not for markers of gestational length, fetal growth, or obstetric conditions that begin during pregnancy. In a second model, we additionally adjusted for gestational hypertension, preeclampsia, gestational diabetes, and abnormal fetal growth (large for gestational or small for gestational age). Finally, we adjusted for delivery attendant as well as hospital fixed effects and accounted for correlation of patients within hospitals with a robust standard error. We conducted a sensitivity analysis restricting models to term (37 weeks) gestation to evaluate whether associations differed in the subset of term, first-birth cesarean deliveries used as a national quality measure for childbirth care [36]. Results The study population of 216,481 women was 32.7% White, 20.8% Black, 30.0% Hispanic, and 16.4% Asian (Table 1). Black and Hispanic women had the highest prevalence of overweight (28.3% and 27.2%, respectively) and obesity (24.1% and 17.8%). Mean (SD) prepregnancy BMI ranged from 22.5 kg/m2 (3.4 kg/m2) among Asian women to 26.8 kg/m2 (6.1 kg/m2) among Black women. Mean gestational weight gain and prevalence of excessive gain were similar across racial and ethnic groups. Women who were overweight or obese were more likely to undergo induced labor or prelabor cesarean versus spontaneous labor (Supplementary Material, Table S2). Births in 2010, which were excluded because of record linkage errors, did not differ from those included in terms of sociodemographic and medical characteristics identifiable in birth certificates (data not shown). Thirty-one percent (n ¼ 66,820) of women in the study population had a cesarean delivery. Of these, 24.8% (n ¼ 16,560) were prelabor cesareans, 32.4% (n ¼ 21,641) followed spontaneous labor, and 42.8% (n ¼ 28,619) followed labor induction (data not shown in table). In addition, 35.3% of Black women had a cesarean delivery,

followed by 30.9% of Asian, 29.8% of Hispanic, and 29.0% of White women (Table 2). We confirmed a pattern of increasing cesarean prevalence with increasing BMI class in each racial and ethnic group and for each labor and delivery pathway (Fig. 1). Women with BMI 25 kg/m2 were roughly 1.4e1.5 times more likely to have a cesarean delivery than women with a BMI in the normal range after adjusting for sociodemographic and prepregnancy characteristics (Table 2). Absolute risk increases ranged from 9% to 13% by race and ethnicity. Associations showed significant statistical heterogeneity (Pheterogeneity < .001 on relative and absolute scales) but were qualitatively similar across racial and ethnic groups. The PAF (95% CI) for risk attributable to elevated BMI was 6.8% (6.2%e7.3%) among Asian, 10.9% (10.4%e11.4%) among White, 14.6% (13.7%e15.5%) among Hispanic, and 17.4% (16.2%e18.6%) among Black women. Over the 5 years of NYC births included in this study, these proportions imply the potential for prevention of roughly 8500 singleton, primary cesarean deliveries (2827 among Hispanic, 2770 among Black, 2239 among White, and 747 among Asian women) if overweight and obese women had the cesarean risk of women with a BMI in the normal range. PAF patterns were not markedly different across obstetric trajectories defined by spontaneous labor, induced labor, or prelabor cesarean delivery (Supplementary Material, Table S3). Examination of Asian subgroups indicated that the lower PAF among Asian women was driven by the low prevalence of overweight and obesity among East Asians (10% compared with 23% among Southeast Asian/Pacific Islander and 30% among Asian Indians), who constitute more than half of the Asian population in NYC (Supplementary Material, Table S4). The positive doseeresponse association between disaggregated BMI class and cesarean delivery was strongest among White and weakest among Asian women (Table 3, Model 1). Associations were partially attenuated with adjustment for downstream weightrelated obstetric complications (Model 2), and the stronger risk gradient among White women was eliminated after accounting for hospital-level fixed effects (Model 3). Table 3 displays associations for each variable, race and BMI, within strata of the other and shows that in almost every stratum of BMI, the risk of cesarean delivery was higher among non-White compared with White women. We found negligible differences in magnitude and no difference in patterns of associations by race and ethnicity or BMI subgroup when restricted to term births (data not shown). Discussion In a diverse population of more than 200,000 nulliparous women with a live singleton birth in NYC from 2008 to 2013,

Table 2 Risk ratios, risk differences, and attributable fractions for cesarean delivery comparing overweight/obese to normal weight nulliparous women delivering in New York City, 2008e2013, stratified by maternal race/ethnicity, n ¼ 216,481 Race or ethnicity

Births by race/ ethnicity, N

Overweight/ obesity prevalence, %

CD prevalence, %

CD prevalence among WNW, %

CD prevalence among WOO, %

Risk ratio (95% CI)*

Risk difference (95% CI)*

Attributable fraction (%) (95% CI) among WOOy

Population attributable fraction (%) (95% CI)z

White Black Hispanic Asian

70,836 45,100 64,980 35,565

24.2 52.5 45.0 18.1

29.0 35.3 29.8 30.9

26.0 28.2 25.1 28.8

38.7 41.7 35.5 40.7

1.51 1.39 1.37 1.40

0.13 0.11 0.09 0.12

33.7 28.1 27.2 28.4

10.9 17.4 14.6 6.8

(1.47e1.54) (1.35e1.43) (1.34e1.41) (1.35e1.45)

(0.12e0.13) (0.10e0.12) (0.09e0.10) (0.10e0.13)

(32.2e35.3) (26.2e30.0) (25.5e29.0) (25.9e30.8)

(10.4e11.4) (16.2e18.6) (13.7e15.5) (6.2e7.3)

CD ¼ cesarean delivery; WNW ¼ women of normal weight; WOO ¼ women with overweight/obesity. * Measures of association comparing women with overweight and obesity to women of normal weight. Models adjusted for maternal age, educational attainment, insurance coverage, pre-existing diabetes, pre-existing hypertension, and year of delivery in multivariable regression models. y Percentage of CD among women with overweight/obesity because of high BMI, by racial/ethnic group, calculated as follows: AF ¼ ([RR  1]/RR), where RR is adjusted risk ratio comparing overweight/obese to normal weight women within each racial/ethnic group. z Percentage of CD among all women because of high BMI, by racial/ethnic group, calculated as follows: PAF ¼ pd ([RR  1]/RR), where RR is adjusted risk ratio comparing overweight/obese to normal weight women within each racial/ethnic group and pd is the proportion of cesarean delivery cases that were among women with overweight or obesity.

Please cite this article as: Glazer KB et al., Elucidating the role of overweight and obesity in racial and ethnic disparities in cesarean delivery risk, Annals of Epidemiology, https://doi.org/10.1016/j.annepidem.2019.12.012

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Fig. 1. Prevalence of primary cesarean delivery among 216,481 nulliparous women delivering in New York City hospitals, by prepregnancy BMI and race/ethnicity, 2008e2013. The denominator for calculation of prevalence of any cesarean delivery and for prelabor cesarean delivery was all live births in the study population. Calculations for cesarean prevalence following labor induction and spontaneous labor included only those women who experienced the respective labor pathway.

increasing BMI was associated with increasing risk of cesarean delivery in each of four racial and ethnic groups, with the strongest gradient among White women. When accounting for overweight and obesity prevalence by race and ethnicity, the proportion of cesarean risk attributable to elevated BMI was largest among Black women. Our study adds to the literature explaining racial disparities in cesarean rates in the United States. Studies report that unadjusted rates of cesarean delivery are similar or slightly lower among non-White compared with White women [9,10,12,23,37], but that risk is increased among women of color after adjustment for a range of sociodemographic, medical, and obstetric characteristics [2,9,10,12]. However, most research either has not adjusted for BMI or has not explored the role of BMI apart from other risk factors. A limited body of work has explored the converse association between BMI and cesarean risk by race and ethnicity, similar to that we have done here [2,8]. Our finding of a stronger association between BMI and cesarean risk among White compared with minority women was contrary to

our expectations. Variation in underlying pathophysiological mechanisms may contribute to this result. Asian women tend to have higher body fat percentages at lower BMIs and higher concentrations of visceral adipose tissue, a predictor of cardiometabolic disorders, than White women of the same BMI [25]. Women of color are at higher risk for gestational diabetes and preeclampsia at lower BMIs than White women [2,26]. In our analyses, adjustment for gestational complications partially attenuated the pronounced risk gradient observed among White women. This pattern supports the explanation that obesity is a stronger independent determinant of cesarean delivery among White women compared with other racial and ethnic groups in part because women of color are at higher risk at lower BMIs for comorbidities that often result in interventional delivery. A prior study of obesity and perinatal outcomes similarly reported a stronger gradient of cesarean delivery risk among White women [2] but did not address the extent to which associations were attributable to source of care. The inclusion of type of delivery attendant and hospital effects in our regression models balanced

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Table 3 Risk ratios for associations between prepregnancy BMI class, race/ethnicity, and cesarean delivery among nulliparous women delivering in New York City hospitals, 2008e2013, n ¼ 216,481 Modification by race/ethnicity of the association between BMI and risk of primary CD Non-Hispanic White

Non-Hispanic Black

Hispanic

Asian

Ref 1.37 (1.33e1.41) 1.79 (1.73e1.85) 2.23 (2.07e2.39)

Ref 1.25 (1.21e1.29) 1.51 (1.47e1.56) 1.83 (1.75e1.92)

Ref 1.24 (1.21e1.28) 1.53 (1.49e1.58) 1.90 (1.80e2.01)

Ref 1.35 (1.30e1.40) 1.57 (1.48e1.67) 1.62 (1.27e2.06)

Ref 1.32 (1.28e1.36) 1.66 (1.60e1.72) 2.05 (1.89e2.21)

Ref 1.23 (1.19e1.27) 1.47 (1.42e1.52) 1.75 (1.66e1.85)

Ref 1.21 (1.18e1.25) 1.47 (1.43e1.52) 1.77 (1.67e1.89)

Ref 1.31 (1.25e1.36) 1.47 (1.38e1.57) 1.35 (0.97e1.88)

Ref 1.27 (1.24e1.30) 1.56 (1.50e1.62) 1.76 (1.62e1.91)

Ref 1.21 (1.18e1.25) 1.43 (1.39e1.48) 1.65 (1.57e1.73)

Ref 1.21 (1.171.24) 1.43 (1.39e1.48) 1.69 (1.59e1.79)

Ref 1.28 (1.22e1.33) 1.41 (1.32e1.51) 1.36 (1.01e1.81)

*

Model 1 Normal weight Overweight Obese class I/II Obese class III Model 2y Normal weight Overweight Obese class I/II Obese class III Model 3z Normal weight Overweight Obese class I/II Obese class III

Modification by BMI of the association between race/ethnicity and risk of primary CD Normal weight

Overweight

Obese class I/II

Obese class III

White Black

Ref 1.42 (1.39e1.46) 1.29 (1.26e1.32) 1.18 (1.15e1.21)

Ref 1.27 (1.23e1.32) 1.16 (1.12e1.20) 1.19 (1.14e1.24)

Ref 1.15 (1.11e1.20) 1.05 (1.01e1.10) 1.07 (1.00e1.14)

Ref 1.05 (0.97e1.14) 0.98 (0.90e1.07) 0.88 (0.68e1.13)

White Black

Ref 1.42 (1.38e1.46) 1.28 (1.25e1.31) 1.20 (1.18e2.23)

Ref 1.29 (1.25e1.34) 1.16 (1.12e1.21) 1.21 (1.16e1.26)

Ref 1.18 (1.13e1.23) 1.07 (1.03e1.12) 1.08 (1.01e1.16)

Ref 1.04 (0.95e1.14) 0.97 (0.88e1.07) 0.78 (0.56e1.07)

White Black

Ref 1.42 (1.38e1.47) 1.30 (1.26e1.34) 1.19 (1.16e1.22)

Ref 1.29 (1.24e1.34) 1.18 (1.14e1.23) 1.18 (1.13e1.24)

Ref 1.16 (1.11e1.21) 1.09 (1.04e1.14) 1.06 (0.98e1.14)

Ref 1.11 (1.01e1.22) 1.05 (0.95e1.16) 0.90 (0.68e1.20)

*

Model 1 Non-Hispanic Non-Hispanic Hispanic Asian Model 2y Non-Hispanic Non-Hispanic Hispanic Asian Model 3z Non-Hispanic Non-Hispanic Hispanic Asian

CD ¼ cesarean delivery; Ref ¼ reference. Pheterogeneity < .001 from product term for exposure and stratification variables in multivariable regression models; alpha set at P ¼ .05 for statistically significant heterogeneity of associations. * Adjusted for maternal age, educational attainment, insurance coverage, pre-existing diabetes, pre-existing hypertension, and year of delivery in multivariable regression models. y Adjusted for covariates in Model 1 as well as gestational diabetes, gestational hypertension, pre-eclampsia, and small or large for gestational age. z Adjusted for covariates in Model 2 as well as delivery attendant, delivery hospital, and patient clustering within delivery hospital.

the risk gradient among racial and ethnic groups. This finding implicates between-hospital differences in racial and ethnic variation in the association between elevated BMI and cesarean risk. For example, organizational structures and clinical processes in predominantly White-serving hospitals may favor delivery intervention in cases of elevated BMI. Our data set did not include information on hospital delivery volume, teaching status, staffing practices, or clinical protocols (e.g., labor induction, fetal heart monitoring, and time in labor [38,39]). Disentangling the influence of individual hospital characteristics would help to inform health service and policy interventions. When considering the influence of race on cesarean delivery risk, disparities were largest in the normal weight category, attenuated with increasing BMI, and persisted beyond adjustment for pregnancy complications. These results suggest efforts to limit excessive obstetric intervention in generally low-risk cases to reduce disparities. Further, the higher cesarean risk among minority women was robust to adjustment for delivery hospital. Minority race and ethnicity, therefore, appear to be important predictors of potentially avoidable cesarean deliveries among lowrisk women independent of differences in delivery location. Within-hospital racial and ethnic variation in the quality of delivery care and maternal morbidity has been reported in previous research [40e42]. We did not have information to evaluate the

extent to which individual provider practices, clinical indicators such as Bishop score and oxytocin dosing, or patient preferences account for the disparities among low-risk women. However, a California study found that hospital and physician effects explained only a small portion of the excess risk of cesarean delivery among Black, Hispanic, and Asian compared with White women [14]. Prospective studies incorporating medical record data with patient and clinician perspectives are necessary to document racial and ethnic differences in labor course and childbirth care. Absolute and attributable risk measures are useful but underutilized [43e46] descriptors of population health. We found that relative risk increases of 40%e51% translated to absolute increases of 9e13 additional cesareans per 100 deliveries among women with elevated BMI compared to those with BMI in the normal range. Our estimates are in line with one study reporting risk differences for cesarean delivery associated with overweight and obesity among primiparous women [43]. Patterns in PAFs were driven by the larger number of Hispanic and Black women at elevated risk, with 40%e50% prevalence of overweight and obesity in these groups. We found similar patterns but slightly smaller associations compared with three studies from the United States, Australia, and the United Kingdom with PAFs ranging from 1% to 12% [44e46], potentially because of differences in obesity prevalence, health care delivery systems, and

Please cite this article as: Glazer KB et al., Elucidating the role of overweight and obesity in racial and ethnic disparities in cesarean delivery risk, Annals of Epidemiology, https://doi.org/10.1016/j.annepidem.2019.12.012

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comparison groups. We included overweight and obese patients as “exposed” in PAF estimates because approximately 20% of overweight and obese reproductive-aged women in the United States have a BMI between 25 and 29.9 kg/m2 [47]. Estimates correspond to singleton deliveries among nulliparous women without major contraindications to vaginal delivery, which helps to isolate cases where improved detection and management of gestational complications and changes to labor and delivery practices may reduce cesarean risk. Our study is limited by reliance on maternal recall of prepregnancy weight. A recent review found minimal bias in associations between prepregnancy weight and birth outcomes from reporting error [48]. However, studies document varying accuracy of recall by BMI and racial and ethnic background, including greater underestimation of weight among obese Black than obese White women [48,49]. We expect that exposure misclassification within race and ethnicity would be nondifferential with respect to the study outcome and generally bias results toward the null; PAFs, particularly among Black women, may be larger than reported here. We do not have reason to believe that births excluded for record linkage differed systematically from those included. Finally, we may overadjust models with race as the primary exposure for potential “downstream” demographics (e.g., education and maternal age). However, we aimed to isolate racial disparities in obstetric care independent of other major sociodemographic contributors and did not find induced selection bias using a directed acyclic graph. Our study has several notable strengths. The size and diversity of the NYC population allowed for stratification by racial and ethnic subgroups and BMI classes, as well as separate examination of deliveries by prelabor cesarean and after spontaneous or induced labor. The population-based data set is inclusive of all live births in NYC, minimizing concerns about selection bias. Information on diagnoses and procedures from ICD codes in discharge records is highly specific but potentially prone to inaccuracies from underreporting [50]. Our use of both hospital discharge and birth certificate data improves validity compared with the use of either source alone [29,50,51]. Conclusions We estimated that overweight and obesity contribute to roughly 7%e17% of cesarean deliveries in first births across racial and ethnic groups in NYC. Interventions to limit prepregnancy weight and target the pathobiology of obesity in labor progression (e.g., decreased cervical dilation and uterine contractility) would reduce cesarean risk for women of all racial and ethnic backgrounds and, in particular, Black and Hispanic women because of disproportionate obesity prevalence. However, drivers of obstetric intervention among low-risk women must be clarified and addressed for substantial mitigation of racial and ethnic disparities in cesarean delivery use. Acknowledgments The authors would thank the New York City Department of Health and Mental Hygiene and the New York State Department of Health for providing access to the birth records used to conduct this study and for assistance in data management. References [1] Borrell LN, Rodriguez-Alvarez E, Savitz DA, Baquero MC. Parental race/ ethnicity and adverse birth outcomes in New York City: 2000e2010. Am J Public Health 2016;106:1491e7.

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[41] Howell EA, Egorova NN, Balbierz A, Zeitlin J, Hebert PL. Site of delivery contribution to black-white severe maternal morbidity disparity. Am J Obstet Gynecol 2016;215:143e52. [42] Creanga AA, Bateman BT, Mhyre JM, Kuklina E, Shilkrut A, Mph WMC. Performance of racial and ethnic minority-serving hospitals on delivery-related indicators. Am J Obstet Gynecol 2014;211:647.e1e647.e16. [43] Hermann M, Le Ray C, Blondel B, Goffinet F, Zeitlin J. The risk of prelabor and intrapartum cesarean delivery among overweight and obese women: possible preventive actions. Am J Obstet Gynecol 2015;212:241.e1e9. [44] Cheney K, Farber R, Barratt AL, McGeechan K, de Vries B, Ogle R, et al. Population attributable fractions of perinatal outcomes for nulliparous women associated with overweight and obesity, 1990e2014. Med J Aust 2018;208:119e25. [45] Lu GC, Rouse DJ, DuBard M, Cliver S, Kimberlin D, Hauth JC. The effect of the increasing prevalence of maternal obesity on perinatal morbidity. Am J Obstet Gynecol 2001;185:845e9. [46] Oteng-Ntim E, Kopeika J, Seed P, Wandiembe S, Doyle P. Impact of obesity on pregnancy outcome in different ethnic groups: calculating population attributable fractions. PLoS One 2013;8:1e7. [47] Vahratian A, Siega-Riz AM, Savitz DA, Zhang J. Maternal pre-pregnancy overweight and obesity and the risk of cesarean delivery in nulliparous women. Ann Epidemiol 2005;15:467e74. [48] Headen I, Cohen AK, Mujahid M, Abrams B. The accuracy of self-reported pregnancy-related weight: a systematic review. Obes Rev 2017;18:350e69. [49] Bodnar LM, Abrams B, Bertolet M, Gernand AD, Parisi SM, Himes KP, et al. Validity of birth certificate-derived maternal weight data. Paediatr Perinat Epidemiol 2014;28:203e12. [50] Lain SJ, Hadfield RM, Oxon D, Raynes-Greenow CH, Ford JB, Mealing NM, et al. Quality of data in perinatal population health databases: a systematic review. Med Care 2012;50:e7e20. [51] Gregory ECW, Martin JA, Argov EL, Osterman MJK. Assessing the quality of medical and health data from the 2003 birth certificate revision: results from New York City. Natl Vital Stat Rep 2019;68:1e19.

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Appendix

Table S1 Medical and obstetric characteristics of the study population by experience of prelabor cesarean delivery, onset of spontaneous labor, or use of labor induction, n ¼ 216,481 Variables

Mean ± SD or N (%)a Prelabor cesarean deliveries Non-Hispanic white (n ¼ 5484)

BMI Normal Overweight Obese Class I/II Obese Class III Mean Height (inches) Gestational weight gain, kga Excessive Adequate Inadequate Mean (SD) Delivery hospital Private Public Delivery attendant Physician Certified nurse midwife Other Gestational age at delivery, weeks Late preterm (34e<37) Early term (37e<39) Term (39e<41) Late term (41e42) Postterm (42+) Mean (SD) Diabetic disorders Preexisting diabetes Gestational diabetes Hypertensive disorders Preexisting HTN Gestational HTN Preeclampsia LGA SGA

Non-Hispanic black (n ¼ 4207)

Hispanic (n ¼ 4278)

Asian (n ¼ 2591)

3749 (68.4) 1104 (20.1) 552 (10.1) 79 (1.4) 24.3 ± 4.9 64.6 ± 2.7

1645 1286 1022 254 28.0 64.5

(39.1) (30.6) (24.3) (6.0) ± 6.7 ± 2.8

2068 (48.3) 1210 (28.3) 858 (20.1) 142 (3.3) 26.7 ± 5.9 63.0 ± 2.8

1979 (76.4) 466 (18.0) 140 (5.4) 6 (0.2) 23.1 ± 3.8 62.7 ± 2.4

2423 (44.2) 1571 (28.7) 1490 (27.2) 15.1 ± 6.7

1523 (36.2) 839 (19.9) 1845 (43.9) 13.4 ± 7.8

1593 (37.2) 978 (22.9) 1707 (39.9) 13.9 ± 7.2

997 (38.5) 837 (32.3) 757 (29.2) 13.9 ± 6.1

5357 (97.7) 127 (2.3)

3446 (81.9) 761 (18.1)

3399 (79.5) 879 (20.6)

2352 (90.8) 239 (9.2)

5438 (99.2) 27 (0.5) 19 (0.3)

4187 (99.5) 17 (0.4) 3 (0.1)

4228 (98.8) 39 (0.9) 11 (0.3)

2578 (99.5) 10 (0.4) 3 (0.1)

137 (2.5) 1345 (24.5) 3554 (64.8) 413 (7.5) 35 (0.6) 39.0 ± 1.2

126 (3.0) 1226 (29.1) 2510 (59.7) 327 (7.8) 18 (0.4) 38.9 ± 1.3

113 (2.6) 1101 (25.7) 2703 (63.2) 342 (8.0) 19 (0.4) 39.0 ± 1.2

49 (1.9) 650 (25.1) 1729 (66.7) 155 (6.0) 8 (0.3) 39.0 ± 1.1

68 (1.2) 388 (7.1)

82 (2.0) 331 (7.9)

86 (2.0) 333 (7.8)

30 (1.2) 366 (14.1)

109 (2.0) 152 (2.9) 233 (4.3) 669 (12.2) 593 (10.9)

213 (5.1) 146 (4.0) 361 (9.0) 293 (7.0) 758 (18.0)

128 (3.0) 145 (3.7) 284 (6.8) 493 (11.5) 580 (13.6)

53 (2.1) 56 (2.3) 84 (3.3) 182 (7.0) 401 (15.5)

Deliveries following spontaneous labor

BMI Normal Overweight Obese Class I/II Obese Class III Mean Height (inches) Gestational weight gain, kga Excessive Adequate Inadequate Mean (SD) Delivery hospital Private Public Delivery attendant Physician Certified nurse midwife Other Gestational age at delivery, weeks Late preterm (34e<37) Early term (37e<39) Term (39e<41) Late term (41e42) Postterm (42+)

Non-Hispanic white (n ¼ 39,483)

Non-Hispanic black (n ¼ 24,534)

Hispanic (n ¼ 36,144)

Asian (n ¼ 19,682)

31,150 (78.9) 6056 (15.3) 2072 (5.3) 205 (0.52) 23.0 ± 3.8 64.8 ± 2.6

12,709 (51.8) 6779 (27.6) 4350 (17.7) 696 (2.8) 26.1 ± 5.8 64.7 ± 2.7

20,987 (58.1) 9543 (26.4) 5056 (14.0) 558 (1.5) 25.3 ± 5.0 63.0 ± 2.8

16,523 (84.0) 2550 (13.0) 590 (3.0) 19 (0.1) 22.3 ± 3.2 63.0 ± 2.3

15,141 (38.4) 13,138 (33.3) 11,204 (28.4) 13.9 ± 6.1

8554 (34.9) 5764 (23.5) 10,216 (41.6) 13.1 ± 7.2

12,823 (35.5) 9379 (26.5) 13,942 (38.6) 13.3 ± 6.8

38,048 (96.4) 1435 (3.6)

18,208 (74.2) 6326 (25.8)

26,875 (74.4) 9269 (25.6)

17,514 (89.0) 2168 (11.0)

36,086 (91.4) 3354 (8.5) 43 (0.1)

21,765 (88.7) 2715 (11.1) 54 (0.2)

31,010 (85.8) 5052 (14.0) 82 (0.2)

18,750 (95.3) 913 (4.6) 19 (0.1)

1555 (3.9) 7496 (19.0) 26,529 (67.2) 3667 (9.3) 236 (0.6)

1707 (7.0) 6461 (26.3) 14,675 (59.8) 1623 (6.6) 68 (0.3)

2032 (5.6) 8767 (24.3) 22,776 (63.0) 2464 (6.8) 105 (0.3)

1000 (5.1) 5302 (26.9) 12,171 (61.8) 1140 (5.8) 69 (0.4)

6425 6942 6315 13.4

(32.6) (35.3) (32.1) ± 5.7

(continued on next page)

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Table S1 (continued ) Deliveries following spontaneous labor

Mean (SD) Diabetic disorders Preexisting diabetes Gestational diabetes Hypertensive disorders Preexisting HTN Gestational HTN Preeclampsia LGA SGA

Non-Hispanic white (n ¼ 39,483)

Non-Hispanic black (n ¼ 24,534)

Hispanic (n ¼ 36,144)

Asian (n ¼ 19,682)

39.2 ± 1.3

38.8 ± 1.4

38.9 ± 1.3

38.9 ± 1.3

129 (0.3) 1321 (3.4)

177 (0.7) 1030 (4.2)

172 (0.5) 1419 (3.9)

95 (0.5) 1953 (9.9)

307 (0.8) 797 (2.1) 724 (1.9) 1958 (5.0) 4442 (11.3)

524 (2.1) 778 (3.4) 1329 (5.5) 806 (3.3) 4357 (17.8)

442 (1.2) 1103 (3.2) 1426 (4.0) 1497 (4.1) 4767 (13.2)

155 284 364 513 3068

Non-Hispanic white (n ¼ 25,869)

Non-Hispanic black (n ¼ 16,359)

Hispanic (n ¼ 24,558)

Asian (n ¼ 13,292)

12,671 (51.6) 6897 (28.1) 4302 (17.5) 688 (2.8) 26.1 ± 5.6 62.9 ± 2.9

10,629 (80.0) 2022 (15.2) 609 (4.6) 32 (0.2) 22.7 ± 3.6 63.0 ± 2.2

(0.8) (1.5) (1.9) (2.6) (15.6)

Deliveries following labor induction

BMI Normal Overweight Obese Class I/II Obese Class III Mean Height (inches) Gestational weight gain, kga Excessive Adequate Inadequate Mean (SD) Delivery hospital Private Public Delivery attendant Physician Certified nurse midwife Other Gestational age at delivery, weeks Late preterm (34e<37) Early term (37e<39) Term (39e<41) Late term (41e42) Postterm (42+) Mean (SD) Diabetic disorders Preexisting diabetes Gestational diabetes Hypertensive disorders Preexisting HTN Gestational HTN Preeclampsia LGA SGA

18,800 (72.7) 4683 (18.1) 2075 (8.0) 311 (1.2) 23.8 ± 4.6 64.7 ± 2.7

7086 4709 3755 809 27.4 64.7

(43.3) (28.8) (23.0) (5.0) ± 6.4 ± 2.7

11,059 (42.8) 7739 (30.1) 7071 (27.3) 15.1 ± 6.3

6132 3243 6984 13.65

(37.5) (19.8) (42.7) ± 6.94

25,051 (96.8) 818 (3.2)

11,483 (70.2) 4876 (29.8)

18,193 (74.1) 6365 (25.9)

11,416 (85.9) 1876 (14.1)

24,712 (95.5) 1124 (4.3) 33 (0.1)

14,844 (90.7) 1482 (9.1) 33 (0.2)

22,361 (91.1) 2137 (8.7) 60 (0.2)

12,789 (96.2) 486 (3.7) 17 (0.1)

907 (3.5) 4429 (17.1) 15,205 (58.8) 4870 (18.8) 458 (1.8) 39.1 ± 1.5

1004 (6.1) 3733 (22.8) 8797 (53.8) 2663 (16.3) 162 (1.0) 39.1 ± 1.5

1271 (5.2) 4996 (20.3) 13,765 (56.1) 4292 (17.5) 234 (1.0) 39.2 ± 1.5

161 (0.6) 1411 (5.5)

238 (1.5) 1215 (7.4)

269 (1.1) 1772 (7.2)

136 (1.0) 1940 (14.6)

534 (2.1) 1232 (5.1) 1467 (5.8)

892 (5.5) 943 (7.0) 2257 (14.4)

756 (3.1) 1366 (6.4) 2561 (10.7)

252 (1.9) 387 (3.1) 618 (4.7)

1429 (5.5) 3040 (11.8)

690 (4.2) 3038 (18.6)

1240 (5.1) 3471 (14.2)

407 (3.1) 2276 (17.1)

9361 5850 9347 14.0

(38.1) (23.8) (38.1) ± 7.1

4839 4498 3955 14.0

565 2906 8000 1680 141 39.2

(36.4) (33.8) (29.8) ± 5.8

(4.3) (21.9) (60.2) (12.6) (1.1) ± 1.4

HTN ¼ hypertension; LGA ¼ large for gestational age (birthweight above the 90th percentile for gestational age and sex); PE ¼ preeclampsia; SGA ¼ small for gestational age (birthweight above the 90th percentile for gestational age and sex). a Adequate weight gain (kg) ranges by BMI class per 2009 Institute of Medicine guidelines: 11.5e16 (normal weight), 7e11.5 (overweight), 5e9 (obese).

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Table S2 Risk ratios, risk differences, and attributable fractions for cesarean delivery comparing overweight/obese to normal weight nulliparous women delivering in New York City, 2008e2013, stratified by maternal race/ethnicity and obstetric pathways, n ¼ 216,481 Births in pathway by race/ethnicity, N (%)a

Overweight/ obesity prevalence, %

CD prevalence among WNW, %

Cesarean deliveries among all births White 70,836 24.2 26.0 Black 45,100 52.5 28.2 Hispanic 64,980 45.0 25.1 Asian 35,565 18.1 28.8 Prelabor Cesarean Deliveries among all Births White 70,836 24.2 7.0 Black 45,100 52.5 7.7 Hispanic 64,980 45.0 5.8 Asian 35,565 18.1 6.8 Cesarean Deliveries among Births following Spontaneous Labor White 39,483 (55.7) 21.1 15.1 Black 24,534 (54.4) 48.2 15.8 Hispanic 36,144 (55.6) 41.9 14.6 Asian 19,682 (55.3) 16.1 18.0 Cesarean Deliveries among Births following Labor Induction White 25,869 (36.5) 27.3 29.2 Black 16,356 (36.3) 56.7 33.7 Hispanic 24,558 (37.8) 48.4 30.2 Asian 13,292 (37.4) 20.0 32.3

CD prevalence among WOO, %

Risk ratio (95% CI)b comparing WOO to WNW

Risk difference (95% CI)b comparing WOO to WNW

Attributable fraction (%) (95% CI) among WOOc

Population attributable fraction (%) (95% CI)d

38.7 41.7 35.5 40.7

1.51 1.39 1.37 1.40

(1.47e1.54) (1.35e1.43) (1.34e1.41) (1.35e1.45)

0.13 0.11 0.09 0.12

(0.12e0.13) (0.10e0.12) (0.09e0.10) (0.10e0.13)

33.7 28.1 27.2 28.4

(32.2e35.3) (26.2e30.0) (25.5e29.0) (25.9e30.8)

10.9 17.4 14.6 6.8

(10.4e11.4) (16.2e18.6) (13.7e15.5) (6.2e7.3)

10.1 10.8 7.6 9.5

1.46 1.30 1.26 1.38

(1.38e1.54) (1.22e1.38) (1.19e1.34) (1.26e1.51)

0.03 0.02 0.01 0.03

(0.02e0.03) (0.02e0.03) (0.01e0.02) (0.02e0.04)

31.6 23.0 20.9 27.5

(27.9e35.3) (18.4e27.6) (16.3e25.5) (21.1e33.8)

10.0 14.0 10.8 6.5

(8.8e11.2) (11.2e16.8) (8.4e13.2) (5.0e8.0)

23.2 24.5 21.4 26.0

1.57 1.45 1.43 1.44

(1.50e1.64) (1.38e1.53) (1.37e1.50) (1.35e1.54)

0.09 0.07 0.06 0.08

(0.08e0.10) (0.06e0.08) (0.05e0.07) (0.06e0.10)

36.2 31.1 30.1 30.5

(33.2e39.2) (27.6e34.7) (27.0e33.2) (25.8e35.2)

10.6 18.4 15.5 6.6

(9.7e11.4) (16.3e20.5) (13.9e17.1) (5.6e7.6)

41.9 47.5 41.4 44.7

1.47 1.35 1.34 1.36

(1.42e1.53) (1.30e1.40) (1.30e1.39) (1.30e1.44)

0.13 0.12 0.10 0.12

(0.12e0.15) (0.10e0.13) (0.09e0.12) (0.10e0.14)

32.0 25.9 25.5 26.7

(29.7e34.4) (23.0e28.9) (12.9e15.8) (22.9e30.4)

11.2 16.8 14.4 6.8

(10.4e12.1) (14.9e18.7) (12.9e15.8) (5.9e7.8)

WNW ¼ women of normal weight in each obstetric pathway; WOO ¼ women with overweight/obesity in each obstetric pathway. a Data in column are total N of births in each racial/ethnic group for cesareans among all births and prelabor cesareans, and N (% of births in each racial/ethnic group) for cesarean deliveries following spontaneous and induced labor. b Measures of association comparing women with overweight and obesity to women of normal weight. Models adjusted for maternal age, educational attainment, insurance coverage, preexisting diabetes, preexisting hypertension, and year of delivery in multivariable regression models. c % of CD among women with overweight/obesity due to high BMI, by racial/ethnic group, calculated as follows: AF ¼ [(RR-1)/RR], where RR ¼ adjusted risk ratio comparing overweight/obese to normal weight women within each racial/ethnic group. d % of CD among all women due to high BMI, by racial/ethnic group, calculated as follows: PAF ¼ pd[(RR-1)/RR], where RR ¼ adjusted risk ratio comparing overweight/obese to normal weight women within each racial/ethnic group and pd ¼ proportion of cesarean delivery cases that were among women with overweight or obesity.

Table S3 Risk ratios, risk differences, and attributable fractions comparing overweight/obese and normal weight Asian women delivering in New York City hospitals, 2008e2013, n ¼ 35,565

Asian Indian East Asiana Southeast Asianb

N (%) of Asian populationc

Overweight/ obesity prevalence (%)

CD prevalence among WNWd, %

CD prevalence among WOOe, %

Risk ratio (95% CI)f comparing WOO to WNW

Risk difference (95% CI)f comparing WOO to WNW

Attributable fraction (%) (95% CI) among WOOg

Population attributable Fraction (%)h (95% CI)

9886 (27.8) 20,033 (56.3) 2375 (6.7)

2988 (30.2) 2007 (10.0) 554 (22.5)

2146 (31.1) 4903 (27.2) 585 (31.6)

1204 (40.3) 802 (40.0) 255 (48.9)

1.28 (1.21e1.35) 1.39 (1.31e1.47) 1.45 (1.30e1.62)

0.09 (0.07e0.11) 0.11 (0.09e0.14) 0.14 (0.10e0.19)

21.8 (17.4e26.2) 27.8 (23.6e32.1) 32.7 (25.2e40.1)

7.8 (6.2e9.4) 3.9 (3.3e4.5) 10.0 (7.7e12.2)

a

Chinese, Japanese, Korean. Filipino, Vietnamese. c Percentages do not sum to 100 due to exclusion of ‘other Asian’ (n ¼ 3,182, 9.0%) category for interpretability of results and Pacific Islander (n ¼ 89, <1%) due to insufficient sample size. d Women of normal weight. e Women with overweight/obesity. f Measures of association comparing women with overweight and obesity to women of normal weight. Models adjusted for maternal age, educational attainment, insurance coverage, preexisting diabetes, preexisting hypertension, and year of delivery. g % of CD among women with overweight/obesity due to high BMI, by racial/ethnic group. h % of CD among all women due to high BMI, by racial/ethnic group. b

Please cite this article as: Glazer KB et al., Elucidating the role of overweight and obesity in racial and ethnic disparities in cesarean delivery risk, Annals of Epidemiology, https://doi.org/10.1016/j.annepidem.2019.12.012

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K.B. Glazer et al. / Annals of Epidemiology xxx (xxxx) xxx

Table S4 ICD-9-CM diagnosis and procedure codes used in variable creation Diagnosis codes Cesarean delivery

Active labor

Labor induction

Preexisting HTN w/superimposed PE Preexisting HTN (w/o PE)

PE (w/o HTN) Mild Severe Gestational HTN w/o HTN or PE Preexisting diabetes GDM

Procedure codes 74.0 (classical cesarean section) 74.1 (low cervical cesarean section) 74.2 (extraperitoneal cesarean section) 74.4 (cesarean section of unspecified type), 74.99 (other cesarean section of unspecified type

653.xx (disproportion) 660.xx (obstructed labor) 661.xx (abnormality of forces of labor) 662.xx (long labor) 652.1x (breech or other malpresentation successfully converted to cephalic presentation) 659.0x, 659.1x (failed induction of labor) 656.3x (fetal distress) 663.xx (cord complications during labor and delivery) 644.2 (spontaneous onset of labor before 37 weeks gestation) 649.8 (spontaneous onset of labor after 37 completed weeks of gestation but before 39 completed weeks gestation, with delivery by (planned) cesarean section) 659.2 (maternal pyrexia during labor) 659.3 (generalized infection during labor) 665.1 (rupture of uterus during labor) failed induction of labor (659.0x, 659.1x)

73.1 (other surgical induction of labor) 73.01 (induction of labor by artificial rupture of membranes) 73.4 (medical induction of labor)

642.70e642.74 401.0, 401.1, 401.9, 402.0, 405.01, 405.09, 405.11, 405.19, 405.91, 405.99, 416.0, 459.30, 459.31, 459.32, 459.33, 459.39, 642.00e642.04, 642.10e642.14, 642.20e642.24 642.40e642.44 642.50e642.54, 642.60e642.64 642.30e642.34, 642.90e642.94 250.00e250.93, 648.00e648.04 648.8x

GDM ¼ gestational diabetes mellitus; HTN ¼ hypertension; PE ¼ preeclampsia.

Please cite this article as: Glazer KB et al., Elucidating the role of overweight and obesity in racial and ethnic disparities in cesarean delivery risk, Annals of Epidemiology, https://doi.org/10.1016/j.annepidem.2019.12.012