Objective
Our objective was to explore the trends in prepregnancy body mass index (BMI) for black and white teenagers over time and the association between elevated BMI and outcomes based on race.
Study Design
This was a retrospective cohort study of singleton infants (n = 38,158) born to black (34%) and white (66%) teenagers (<18 years of age). We determined the prevalence of elevated prepregnancy BMI between 1993 and 2006 and the association between elevated prepregnancy BMI (primary exposure) and maternal and perinatal outcomes based on race (2000-2006).
Results
The percentage of white teenagers with elevated prepregnancy BMI increased significantly from 17-26%. White and black overweight and obese teenagers were more likely to have pregnancy-related hypertension than normal-weight teenagers; postpartum hemorrhage was increased only in obese black teenagers, and infant complications were increased only in overweight and obese white teenagers.
Conclusion
Because the percentage of elevated prepregnancy BMI has increased in white teenagers, specific risks for poor maternal and perinatal outcomes in the overweight and obese teenagers varies by race.
Although the rate of teenaged pregnancies in the United States has declined from its peak of 61.8 per 1000 in 1991, recent data suggest that teenaged pregnancy is still a sizable problem, with 34.3 births per 1000 teenagers. Black/white racial disparities in teenaged pregnancy are well-described, with a rate of 51.5 per 1000 black teenagers vs 23.5 per 1000 white teenagers. In addition to the well-described negative psychologic and socioeconomic impact on the teenagers themselves, infants born to teen mothers are more likely to be born preterm and/or low birthweight and have an increased risk of infant death.
Although >16% of female teenagers are overweight or obese, racial differences in obesity have also been identified, with 15.4% of white and 25.4% of black teenagers being overweight or obese. Regardless of race, the implications of being overweight or obese in the teenaged years has been described as a critical time that leads to long-term physiologic and behavioral changes. As the obesity epidemic continues, obesity among pregnant teenagers is becoming increasingly common; 1 study found that 40% of teenaged mothers were overweight or obese.
Overweight and obese pregnant teenagers are more likely to have obstetric complications that include primary cesarean delivery, induction of labor, gestational hypertension, preeclampsia, and gestational diabetes mellitus. Evidence suggests that infants who are born to these teenagers are also more likely to have complications that include postterm delivery, low birthweight, or macrosomia.
In light of the known racial disparities in obesity and teenaged pregnancy, we sought to explore the trends in prepregnancy body mass index (BMI) for black and white teenagers and the association between increasing BMI and maternal and perinatal outcomes. We hypothesized that overweight and obesity have increased in both black and white teenagers and that these teenagers with an elevated prepregnancy BMI are more likely to have perinatal complications. In addition, we hypothesize that an increasing BMI will have a greater detrimental impact in black vs white teenagers that can explain, to some extent, ongoing disparities in outcomes for these teenagers.
Materials and Methods
We conducted a population-based retrospective cohort study of all singleton live infants born in Missouri between 1993 and 2006. Data were obtained from Missouri birth certificate records that are linked to hospital discharge data. We included nulliparous black and white teenagers who were 11-17 years of age to allow for sufficient sample size to assess racial disparities. The exclusion criterion was major congenital anomalies (295 girls; 1.3%). We excluded from the analyses all births that were missing information on maternal prepregnancy BMI (2105 girls; 5.2%). Finally, we excluded mothers who were 18 and 19 years old. Although this is designed as an assessment of teenaged pregnancy, these older teenagers were less likely to be white ( P < .001) and to have higher BMI ( P < .001). In addition, they were more likely to be receiving Medicaid, to smoke, and to be married; therefore, we chose to provide an analysis of a more conservative definition of teenaged pregnancy .
The primary predictor of interest was prepregnancy BMI that was categorized with the use of the Centers for Disease Control and Prevention growth charts for BMI-for-age. Prepregnancy BMI is based on birth certificate documentation of prepregnancy weight and height, which generally is based on self-report and shown to be valid. BMI is calculated as the weight in kilograms divided by the height in meters squared. Growth charts identify percentiles based on BMI for children 2-20 years of age. The Institute of Medicine and Fernandez et al have suggested that the Institute of Medicine criteria for prepregnancy weight categories are inappropriate for adolescents; therefore, we have chosen to report findings using the Centers for Disease Control and Prevention age-specific BMI classification. Teenagers were classified as underweight (BMI <5th percentile), normal (BMI 5th≤ and <85th percentile), overweight (BMI ≤85th and <95th percentile), and obese (BMI ≥95th percentile).
Hospital discharge data on outcomes was available only for deliveries from 2000-2006. Therefore, we limited outcome analyses to this subpopulation. Maternal outcomes included method of delivery, pregnancy-related hypertension, and postpartum hemorrhage, based on previous literature. Method of delivery is categorized on the Missouri birth certificate record as vaginal, vaginal birth after previous cesarean section, repeat cesarean, primary elective cesarean, and primary emergency cesarean. The birth certificate also includes data on the use of outlet/low forceps, mid/high forceps, and vacuum extraction; all of which were categorized as “operative” vaginal delivery. Pregnancy-related hypertension included gestational hypertension, pregnancy-induced hypertension, preeclampsia, and eclampsia. We were unable to examine gestational diabetes mellitus as a primary outcome because the Missouri birth certificate does not clearly differentiate between gestational and types I and II diabetes mellitus. Maternal outcomes were considered present if documented in either the birth certificate or the hospital discharge data.
Gestational age at birth was based on the clinical estimate of gestational age on the birth certificate and categorized as preterm (24 to <37 weeks), term (37-40 weeks), and prolonged (41/42 weeks). Other perinatal outcomes were limited to term infants and included birthweight that was categorized as macrosomic (≥4000 g) or low birthweight (<2500 g). We also created a composite infant complication score that included low Apgar score (<7 at 5 minutes), birth trauma, shoulder dystocia, prolonged length of hospital stay (>5 days), infection, hypoglycemia, polycythemia, respiratory distress syndrome, meconium aspiration syndrome, and seizures. Infant outcomes were obtained exclusively from the birth certificate.
Several maternal sociodemographic characteristics have been shown to be associated with maternal obesity and were evaluated as potential confounders in this study. Given the increasing risk of complications that are associated with decreasing age, maternal age was left as a continuous variable. Maternal education was categorized as high, average, or low on the basis of age and years of education. With the Revised-Graduated Prenatal Care Utilization Index (R-GINDEX), prenatal care was categorized as no care, inadequate, adequate, intermediate, intensive, or missing based on when prenatal care was initiated, total number of prenatal care visits, and gestational age at delivery. Other potential confounders included smoking status (yes vs no/unknown), marital status (married vs not married), insurance status (Medicaid vs private), and infant sex (male vs female). Both chronic hypertension (ICD-9 codes 401, 642.0, 642.1, or 642.2) and diabetes (ICD-9 code 250 or 648.0) were present if there was documentation in either the birth certificate record or the hospital discharge data.
Assessment of trend over time was determined with the use of the Cochran-Armitage test of trend. Bivariate analyses were completed with chi-square test or Fisher exact test, as appropriate. Multivariable logistic regression was used to calculate adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for various outcomes that were stratified by maternal race. Regression models were adjusted a priori for maternal age, education, smoking status, marital status, level of prenatal care, insurance status, maternal diabetes mellitus, maternal chronic hypertension, and infant gender unless otherwise indicated. Multivariate analyses for the method of delivery were performed with the use of multinomial logistic regression analyses. All analyses were completed using SAS software (version 9.1; 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
The final study cohort included 34,648 teenagers (68% white and 32% black). White teenagers were more likely to be older and nulliparous and to report tobacco use; black teenagers were more likely to have poor prenatal care, to be unmarried, and to have lower education ( Table 1 ). Black teenagers were more likely to have chronic hypertension (0.4% in white vs 0.7% in black teenagers; P = .007) and less likely to have diabetes mellitus (1% in white vs 0.7% in black teenagers; P = .05). Overall, black teenagers were more likely to be overweight (19.2%) and obese (11.4%) than were white teenagers (12.6% and 6.6%, respectively; P < .001).
| Characteristic | White (n = 23,576) n (%) | Black (n = 11,072) n (%) |
|---|---|---|
| Maternal age, y a | ||
| ≤14 | 671 (2.9) | 942 (8.5) |
| 15 | 2473 (10.5) | 1890 (17.1) |
| 16 | 6703 (28.4) | 3467 (31.3) |
| 17 | 13,729 (58.2) | 4773 (43.1) |
| Medicaid a | 18,348 (78.1) | 8424 (76.4) |
| Maternal education level a | ||
| High | 7330 (31.3) | 2195 (20.2) |
| Average | 15,888 (67.9) | 8558 (78.7) |
| Low | 194 (0.8) | 123 (1.1) |
| Smoking a | 7193 (30.5) | 571 (5.2) |
| Married a | 3082 (13.1) | 57 (0.5) |
| Prenatal care use a | ||
| Missing | 315 (1.4) | 305 (2.8) |
| None | 1361 (5.8) | 1182 (11.0) |
| Inadequate | 4696 (20.1) | 2211 (20.5) |
| Adequate | 10,621 (45.5) | 4252 (39.4) |
| Intermediate | 5554 (23.8) | 2177 (20.2) |
| Intensive | 820 (3.5) | 653 (6.1) |
| Prepregnancy body mass index a | ||
| Under | 1197 (5.1) | 232 (2.1) |
| Normal | 17,856 (75.7) | 7451 (67.3) |
| Overweight | 2974 (12.6) | 2123 (19.2) |
| Obese | 1549 (6.6) | 1266 (11.4) |
| Male infant | 12,061 (51.2) | 5658 (51.1) |
With regard to trends, the mean prepregnancy BMI for the entire population increased from 22.4 ± 4.3 (SD) in 1993 to 23.4 ± 4.8 in 2006. In 1993, 14.3% of all teenagers were overweight, and another 7.0% were obese. By 2006, 16.9% of all teenagers were overweight, and another 10.8% were obese ( P < .001). The percentage of black teenagers with elevated BMI rose from 29.1% in 1993 to 33.2% in 2006, but this was nonsignificant ( P = .08; Figure 1 ). Specifically, although the mean BMI in black teenagers was stable over time ( P = .161), the percentage of overweight black teenagers rose from 20.1-20.8% ( P = .94), and the percentage of obese black teenagers rose from 10.012.7% ( P = .02). Meanwhile, the percentage of white teenagers with elevated prepregnancy BMI increased significantly between 1993 and 2006 from 17.9-26.1%, respectively ( P < .001). Specifically, the mean BMI increased over time ( P < .001); the percentage of overweight and obese white teenagers increased from 11.3-15.7% ( P < .001) and 5.7-10.4% ( P < .001), respectively.
Complications were evaluated for deliveries between 2000 and 2006 during which there was no significant increase in the percentage of black teenagers with elevated BMI ( P = .64) and a significant increase in percentage of white teenagers with elevated BMI ( P < .001). Overweight and obese white and black teenagers were more likely to have certain maternal and perinatal complications than normal-weight teenagers. We assessed for interaction between race and prepregnancy BMI. Significant interactions were certain outcomes (eg, pregnancy-induced hypertension [ P < .01] and postpartum hemorrhage [ P = .07]); therefore, we present outcomes that are stratified by race ( Tables 2 and 3 ).
| Characteristic | Normal n (%) | Overweight n (%) | Obese n (%) | Adjusted OR a (95% CI) | |
|---|---|---|---|---|---|
| Overweight vs normal | Obese vs normal | ||||
| Maternal complication | |||||
| Pregnancy-related hypertension | 707 (8.8) | 210 (14.6) | 156 (18.8) | 1.70 (1.44–2.02) b | 2.34 (1.92–2.84) b |
| Postpartum hemorrhage | 315 (3.9) | 64 (4.5) | 36 (4.3) | 1.14 (0.87–1.51) | 1.10 (0.77–1.56) |
| Induction | 2519 (31.5) | 541 (37.7) | 318 (38.2) | 1.31 (1.16–1.47) b | 1.33 (1.15–1.54) b |
| Method of delivery | |||||
| Vaginal | 5210 (72.7) | 902 (69.0) | 464 (62.9) | — | |
| Operative vaginal | 796 (11.1) | 120 (9.2) | 58 (7.9) | 0.83 (0.68–1.01) | 0.79 (0.61–1.03) |
| Elective cesarean | 401 (5.6) | 104 (8.0) | 81 (11.0) | 1.46 (1.18–1.81) b | 2.05 (1.61–2.63) b |
| Emergency cesarean | 683 (9.5) | 171 (13.1) | 129 (17.5) | 1.36 (1.15–1.62) b | 2.00 (1.65–2.43) b |
| Birthweight | |||||
| Macrosomia (≥4000 g) | 30 (0.4) | 14 (1.0) | 10 (1.0) | 2.50 (1.32–4.75) b | 2.96 (1.43–6.14) b |
| Low birthweight (<2500 g) | 723 (9.0) | 101 (7.0) | 50 (6.0) | 0.75 (0.60–0.93) | 0.64 (0.47–0.86) b |
| Gestation | |||||
| Preterm (<37 wk) | 797 (10.0) | 121 (8.5) | 89 (10.8) | 0.81 (0.66–0.99) b | 1.05 (0.83–1.33) |
| Prolonged (≥41 wk) | 826 (10.4) | 187 (13.1) | 93 (11.3) | 1.31 (1.10–1.55) b | 1.14 (0.90–1.43) |
| Infant composite c | 1344 (16.8) | 278 (19.4) | 183 (22.0) | 1.19 (1.03–1.37) b | 1.39 (1.17–1.65) b |
a Adjusted for multivariable logistic regression adjusted for maternal age, insurance, education, tobacco use, level of prenatal care, maternal diabetes mellitus, maternal chronic hypertension, and infant sex;
b Indicates statistical significance;
c Infant composite complications include birth trauma, meconium aspiration syndrome, respiratory distress syndrome, length of stay >5 days, and 5-minute Apgar score of <7.
| Characteristic | Normal n (%) | Overweight n (%) | Obese n (%) | Adjusted OR a (95% CI) | |
|---|---|---|---|---|---|
| Overweight vs normal | Obese vs normal | ||||
| Maternal complication | |||||
| Pregnancy-related hypertension | 442 (13.5) | 171 (18.0) | 122 (20.5) | 1.40 (1.15–1.70) b | 1.59 (1.27–2.00) b |
| Postpartum hemorrhage | 97 (3.0) | 41 (4.3) | 30 (5.0) | 1.47 (1.00–2.13) | 1.74 (1.14–2.64)b |
| Induction | 630 (19.2) | 251 (26.5) | 162 (27.2) | 1.54 (1.30–1.83) b | 1.54 (1.26–1.89) b |
| Method of delivery | |||||
| Vaginal | 2443 (74.3) | 663 (69.9) | 386 (64.5) | — | — |
| Operative vaginal | 340 (10.3) | 103 (10.9) | 55 (9.2) | 1.13 (0.89–1.43) | 1.04 (0.77–1.41) |
| Elective cesarean | 208 (6.3) | 71 (7.5) | 57 (9.6) | 1.28 (0.96–1.69) | 1.77 (1.30–2.43) b |
| Emergency cesarean | 296 (9.0) | 111 (11.7) | 98 (16.4) | 1.37 (1.09–1.74) b | 2.10 (1.63–2.71) b |
| Birthweight | |||||
| Macrosomia (≥4000 g) | 5 (0.2) | 6 (0.6) | 1 (0.2) | — | — |
| Low birthweight (<2500 g) | 457 (13.9) | 105 (11.1) | 58 (9.7) | 0.75 (0.60–0.94) | 0.67 (0.50–0.90) b |
| Gestation | |||||
| Preterm (<37 wk) | 424 (13.3) | 116 (12.3) | 63 (10.8) | 0.89 (0.71–1.11) | 0.78 (0.59–.103) |
| Prolonged gestation (≥41 wk) | 304 (9.3) | 116 (12.3) | 81 (13.9) | 1.39 (1.10–1.75) b | 1.51 (1.15–1.97) b |
| Infant composite c | 634 (19.3) | 193 (20.4) | 138 (23.2) | 1.07 (0.89–1.28) | 1.25 (1.00–1.54) |
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