Objective
The purpose of this study was to determine the effect of maternal superobesity (body mass index [BMI], ≥50 kg/m 2 ) compared with morbid obesity (BMI, 40-49.9 kg/m 2 ) or obesity (BMI, 30-39.9 kg/m 2 ) on perinatal outcomes.
Study Design
We conducted a retrospective cohort study of birth records that were linked to hospital discharge data for all liveborn singleton term infants who were born to obese Missouri residents from 2000-2006. We excluded major congenital anomalies and women with diabetes mellitus or chronic hypertension.
Results
There were 64,272 births that met the study criteria, which included 1185 superobese mothers (1.8%). Superobese women were significantly more likely than obese women to have preeclampsia (adjusted relative risk [aRR], 1.7; 95% confidence interval [CI], 1.4–2.1), macrosomia (aRR, 1.8; 95% CI, 1.3–2.5), and cesarean delivery (aRR, 1.8; 95% CI, 1.5–2.1). Almost one-half of all superobese women (49.1%) delivered by cesarean section, and 33.8% of superobese nulliparous women underwent scheduled primary cesarean delivery.
Conclusion
Women with a BMI of ≥50 kg/m 2 are at significantly increased risk for perinatal complications compared with obese women with a lower BMI.
The obesity epidemic remains unabated in the United States. In 2007-2008, 34% of American women who were 20-39 years old met obesity criteria (body mass index [BMI] ≥30 kg/m 2 ) ; obesity is now an increasingly common and harmful pregnancy complication. Superobesity, as coined in the gastric bypass literature to describe patients who weigh ≥225% of ideal body weight, represents individuals with a BMI of ≥50 kg/m 2 . The number of superobese individuals is growing 5 times faster than other obesity categories, which means that healthcare providers increasingly will be challenged to accommodate their healthcare needs.
Obese women are more likely than normal weight women to experience preeclampsia, diabetes mellitus, cesarean delivery, fetal growth abnormalities, and stillbirth. Although several studies compare obese women to normal-weight women, to date there have been limited studies on superobesity in pregnancy. As the number of superobese pregnant women continues to rise, it is important to determine whether there is a “dose-response” relationship between the severity of maternal obesity and perinatal complications.
The objective of this study was to determine the effect of maternal superobesity on perinatal outcomes compared with maternal obesity (BMI, 30-39.9 kg/m 2 ) and morbid obesity (BMI, 40-49.9 kg/m 2 ). We hypothesized that pregnancy in superobese women, compared with obese and morbidly obese women, is associated with (1) increased risk of maternal complications of pregnancy, (2) greater risk of fetal growth abnormalities, and (3) greater risk of infant complications.
Materials and Methods
This was a population-based retrospective cohort study of all liveborn singleton, full-term infants who were born to Missouri residents between January 1, 2000, and December 31, 2006 (N = 502,452). Data were obtained from Missouri vital records, which includes birth certificate records that are linked to hospital discharge information, for the available period of 2000-2006. Women with prepregnancy BMI of ≥30 kg/m 2 were included. Exclusion criteria were documented in the birth certificate or hospital discharge data: (1) fetuses with major congenital anomalies (n = 872; 1.3%) and (2) women with diabetes mellitus (n = 5830; 8.3%) or chronic hypertension (n = 1773; 2.7%). Women with either pregestational or gestational diabetes mellitus were excluded because of the inability to reliably classify the type of diabetes mellitus based on the birth certificate or ICD-9 coding. Inclusion was limited to term infants to avoid confounding of neonatal outcomes that were due to complications that were associated with prematurity.
The primary predictor of interest was maternal BMI. BMI was calculated by self-reported prepregnancy weight in kilograms divided by height in meters squared. The World Health Organization separates obesity (BMI, ≥30 kg/m 2 ) into 3 classes: class I (30-34.9 kg/m 2 ), class II (35.0-39.9 kg/m 2 ), and class III (≥40 kg/m 2 ). Because the objective of this study was to determine the impact of superobesity on perinatal outcomes and whether there was a dose response to increasing obesity, we combined classes I and II as obese (30-39.9 kg/m 2 ) and separated class III into morbid obesity (40-49.9 kg/m 2 ) and superobesity, defined as a BMI of ≥50 kg/m 2 .
The primary outcomes of interest were preeclampsia, method of delivery, macrosomia (birthweight, >4500 g), and composite neonatal morbidity, which included low Apgar score (<7 at 5 minutes), birth trauma, neonatal infection, neonatal hypoglycemia, respiratory distress syndrome, neonatal seizures, neonatal length of stay of >5 days, and/or meconium aspiration syndrome. Low birthweight was defined as <2500 g. If a diagnosis such as preeclampsia, birth trauma, or respiratory distress syndrome was documented in either the birth certificate or the hospital discharge data, then the condition was considered present. Use of the combined birth certificate and hospital discharge data has been found to be more accurate for perinatal outcomes, compared with birth certificate data alone.
Various maternal sociodemographic characteristics have been shown to be associated with maternal obesity and were evaluated as potential confounders in this study. Maternal education was categorized as high, average, or low on the basis of age and years of education. Corrected for maternal age, average education included women within 2 grades of their expected level; low education was ≥2 or more grades below expected grade. Greater than 12 years of education was considered high, regardless of maternal age. The R-GINDEX (University of Manitoba, Winnipeg, Canada) was used to categorize prenatal care as no care, inadequate care, adequate care, intermediate care, intensive care, or missing based on initiation of prenatal care, total number of visits, and gestational age at delivery. Smoking status was determined by maternal self-report on birth certificate records.
Bivariate analyses were completed with the χ 2 test, Fisher’s exact test, and t test, as appropriate. Outcomes were assessed with the Cochrane-Armitage test for linear trend and multivariable regression for adjusted risk. Multivariable logistic regression models were used to evaluate outcomes and were controlled for maternal age, race, parity, smoking status, marital status, Medicaid use, prenatal care, level of education, primary scheduled cesarean delivery, and repeat cesarean delivery. Mode of delivery was categorized by birth certificate designation as vaginal, operative vaginal, vaginal birth after cesarean delivery (VBAC), primary emergent cesarean delivery, primary elective cesarean delivery, and repeat cesarean delivery. For clarity, primary elective cesarean delivery is referred to as primary scheduled cesarean delivery. Comparisons were made among BMI groups (obese, morbidly obese, and superobese). Adjusted relative risk (aRR) and 95% confidence interval were calculated. A probability value of < .05 on 2-tailed tests was considered significant.
All analyses were completed with SAS software (version 9.2; SAS Institute Inc, Cary, NC). Approval for human subject research and a waiver of informed consent were received from the Institutional Review Board at Saint Louis University and the Missouri Department of Health and Senior Services, Section for Epidemiology for Public Health Practice.
Results
There were 64,272 births that met the study criteria: 53,032 women (82.5%) were obese; 10,055 women (15.6%) were morbidly obese, and 1185 women (1.8%) were superobese. Increasing, BMI was associated with increased parity, single status, Medicaid use, African American race, intensive prenatal care usage, and previous cesarean delivery ( Table 1 ). Lower BMI was associated with smoking and higher education levels.
| Maternal body mass index | |||
|---|---|---|---|
| Variable | Obese 30-39.9 kg/m 2 | Morbid 40-49.9 kg/m 2 | Super ≥50 kg/m 2 |
| Maternal race, n (%) a | |||
| African American | 9222 (17.4) | 2178 (21.7) | 376 (31.8) |
| White | 41,143 (77.7) | 7512 (74.9) | 760 (64.3) |
| Hispanic | 1962 (3.7) | 259 (2.6) | 30 (2.5) |
| Asian/other | 621 (1.2) | 86 (0.9) | 16 (1.4) |
| Maternal age, n (%) a | |||
| <18 y | 896 (1.7) | 81 (0.8) | 5 (0.4) |
| 18-34 y | 46,806 (88.3) | 8972 (89.2) | 1053 (88.9) |
| ≥35 y | 5330 (10.0) | 1001 (10.0) | 127 (10.7) |
| Education, n (%) a | |||
| High | 25,482 (48.3) | 4619 (46.1) | 506 (42.9) |
| Average | 19,683 (37.3) | 3971 (39.7) | 489 (41.5) |
| Low | 7563 (14.3) | 1418 (14.2) | 184 (15.6) |
| Married, n (%) a | 34,458 (65.0) | 6370 (63.4) | 664 (56.1) |
| Parity, n (%) a | |||
| 0 | 17,013 (32.2) | 2993 (30.0) | 296 (25.1) |
| 1 | 18,470 (35.0) | 3574 (35.8) | 437 (37.0) |
| 2 | 10,510 (19.9) | 2020 (20.2) | 256 (21.7) |
| ≥3 | 6773 (12.8) | 1398 (14.0) | 192 (16.3) |
| Smoking status, n (%) b | |||
| Yes | 9378 (17.7) | 1685 (16.8) | 167 (14.1) |
| No | 43,368 (81.8) | 8319 (82.7) | 1013 (85.5) |
| Unknown | 286 (0.5) | 51 (0.5) | 5 (0.4) |
| Medicaid, n (%) a | 25,331 (47.9) | 5341 (53.3) | 743 (63.1) |
| Prenatal care use, n (%) a | |||
| Missing | 774 (1.5) | 151 (1.5) | 18 (1.6) |
| None | 258 (0.5) | 46 (0.5) | 7 (0.6) |
| Inadequate | 2327 (4.5) | 417 (4.2) | 54 (4.7) |
| Adequate | 27,928 (53.7) | 5307 (53.9) | 611 (52.9) |
| Intermediate | 16,808 (32.3) | 3056 (31.0) | 344 (29.8) |
| Intensive | 3891 (7.5) | 877 (8.9) | 121 (10.5) |
| Male infant, n (%) | 27,122 (51.1) | 5127 (51.0) | 594 (50.1) |
| Gestational age, wk c | 38.8 ± 1.0 | 38.7 ± 1.0 | 38.7 ± 1.0 |
| Birthweight, g c , d | 3460.6 ± 476.3 | 3490.1 ± 499.5 | 3517.6 ± 514.8 |
c Data are given as mean ± SD;
Increasing maternal BMI was associated with a statistically significant increase in all studied perinatal outcomes, including preeclampsia, macrosomia, and composite neonatal morbidity, except for birth trauma ( Table 2 ). Superobese women were significantly more likely than obese women to have preeclampsia (aRR, 1.7), macrosomia (aRR, 1.9) and neonatal hypoglycemia (aRR, 2.0; Table 3 ). Compared with morbidly obese women, superobese women remained at increased risk for composite neonatal morbidity (aRR, 1.2; P = .02). There was no difference between morbidly obese and superobese women regarding risk for preeclampsia, macrosomia, or neonatal length of stay of >5 days. Compared with obese women, morbidly obese women were at increased risk for these outcomes along with neonatal hypoglycemia and composite neonatal morbidity.
| Body mass index, n (%) | ||||
|---|---|---|---|---|
| Variable | Obese 30-39.9 kg/m 2 | Morbid 40-49.9 kg/m 2 | Super ≥50 kg/m 2 | P value a |
| Preeclampsia | 3842 (7.2) | 980 (9.8) | 129 (10.9) | < .0001 |
| Neonatal length of stay >5 d | 1629 (3.1) | 381 (3.8) | 53 (4.5) | < .0001 |
| Low Apgar score | 343 (0.7) | 67 (0.7) | 15 (1.3) | .05 |
| Macrosomia | 979 (1.9) | 262 (2.6) | 40 (3.4) | < .0001 |
| Low birthweight | 1074 (2.0) | 223 (2.2) | 31 (2.6) | .04 |
| Neonatal hypoglycemia | 1035 (2.0) | 274 (2.7) | 45 (3.8) | < .0001 |
| Birth trauma | 1716 (3.2) | 348 (3.5) | 41 (3.5) | .12 |
| Composite neonatal | 4924 (9.3) | 1097 (10.9) | 153 (12.9) | < .0001 |
| Morbid vs obese | Super vs obese | Super vs morbid | ||||
|---|---|---|---|---|---|---|
| Variable | Adjusted relative risk a (95% CI) | P value | Adjusted relative risk a (95% CI) | P value | Adjusted relative risk a (95% CI) | P value |
| Preeclampsia | 1.4 (1.3–1.5) | < .0001 | 1.7 (1.4–2.1) | < .0001 | 1.2 (1.0–1.4) | .11 |
| Neonatal length of stay >5 d | 1.2 (1.1–1.3) | .003 | 1.3 (1.0–1.8) | .04 | 1.2 (0.9–1.6) | .36 |
| Low Apgar score | 1.0 (0.8–1.4) | .75 | 1.9 (1.1–3.2) | .02 | 1.9 (1.0–3.4) | .04 |
| Macrosomia (≥4500 g) | 1.4 (1.2–1.6) | < .0001 | 1.8 (1.3–2.5) | .0006 | 1.3 (0.9–1.8) | .16 |
| Low birthweight | 1.1 (0.9–1.3) | .24 | 1.3 (0.9–1.9) | .16 | 1.3 (0.9–1.9) | .22 |
| Neonatal hypoglycemia | 1.4 (1.2–1.6) | < .0001 | 2.0 (1.5–2.7) | < .0001 | 1.4 (1.0–1.9) | .05 |
| Birth trauma | 1.2 (1.0–1.3) | .008 | 1.3 (1.0–1.8) | .09 | 1.1 (0.8–1.6) | .44 |
| Composite neonatal morbidity | 1.2 (1.1–1.3) | < .0001 | 1.5 (1.2–1.8) | < .0001 | 1.2 (1.0–1.5) | .02 |
a Adjusted for smoking, Medicaid, age (18-34 years), education (average), prenatal care (adequate), married, nulliparous, repeat cesarean delivery, scheduled primary cesarean delivery, and race.
Increasing maternal obesity was associated significantly with an elevated risk of cesarean delivery and a decreased incidence of vaginal delivery, regardless of parity ( Table 4 ). Among nulliparous women, 31% of superobese women delivered vaginally compared with 53% of obese women; 33.8% of nulliparous superobese women underwent scheduled cesarean delivery. Of the 196 nulliparous superobese women who attempted a vaginal delivery, 94 women (48%) had a spontaneous vaginal birth; 24 women (12%) had an operative vaginal delivery, and 78 women (40%) were delivered by cesarean section. For multiparous women, previous vaginal birth was associated with a significantly decreased risk of emergency cesarean delivery, but most women with a previous cesarean delivery underwent a repeat cesarean delivery, with only 2% of women in each obesity class having a VBAC.
| Body mass index, n (%) | ||||
|---|---|---|---|---|
| Variable | 30-39.9 kg/m 2 | 40-49.9 kg/m 2 | ≥50 kg/m 2 | P value a |
| Nulliparous pregnancy | ||||
| Vaginal delivery | 9042 (53.2) | 1331 (44.5) | 94 (31.8) | < .0001 |
| Operative vaginal delivery | 1747 (10.3) | 268 (9.0) | 24 (8.1) | .0471 |
| Primary scheduled cesarean delivery | 3033 (17.8) | 654 (21.9) | 100 (33.8) | < .0001 |
| Primary emergency cesarean delivery | 3163 (18.6) | 735 (24.6) | 78 (26.4) | < .0001 |
| Multiparous pregnancy | ||||
| Vaginal delivery | 22,334 (62.5) | 3690 (52.8) | 421 (47.6) | < .0001 |
| Operative vaginal delivery | 1343 (3.8) | 272 (3.9) | 39 (4.4) | .3187 |
| Vaginal birth after cesarean delivery | 735 (2.1) | 150 (2.2) | 23 (2.6) | .3073 |
| Primary scheduled cesarean delivery | 1382 (3.9) | 328 (4.7) | 46 (5.2) | .0003 |
| Primary emergency cesarean delivery | 1400 (3.9) | 323 (4.6) | 49 (5.5) | .0004 |
| Repeat scheduled cesarean delivery | 8559 (23.9) | 2229 (31.9) | 307 (34.7) | < .0001 |
| Totals | ||||
| Vaginal delivery | 31,534 (59.5) | 5053 (50.3) | 517 (43.6) | < .0001 |
| Operative vaginal delivery | 3108 (5.9) | 548 (5.5) | 63 (5.3) | .0837 |
| Cesarean delivery | 17,653 (33.3) | 4304 (42.8) | 582 (49.1) | < .0001 |
| Primary scheduled | 4452 (8.4) | 992 (9.9) | 147 (12.4) | < .0001 |
| Primary emergency | 4580 (8.6) | 1067 (10.6) | 127 (10.7) | < .0001 |
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