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ORIGINAL RESEARCH |
From the Medical and Health Research Association of NYC, Inc., and Mailman School of Public Health, Columbia University, New York, New York.
Address reprint requests to: Terry J. Rosenberg, PhD, Medical and Health Research Association of NYC, Inc., 40 Worth Street, Suite 720, New York, NY 10013; E-mail: trosenberg{at}mhra.org.
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ABSTRACT |
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METHODS: Data were from the 1998–1999 New York City births file for 213,208 singletons with information on prepregnancy weight. Five categories of prepregnancy weight were constructed and used to predict gestational diabetes, preeclampsia, cesarean delivery, very low birthweight, macrosomia, and treatment in the neonatal intensive care unit (NICU). Statistical adjustments were made for mother’s age, race or ethnicity, marital status, education, parity, social risk (eg, smoking), initiation of prenatal care, health insurance, and infant’s sex.
RESULTS: Maternal prepregnancy weight was associated with several adverse outcomes. Women in the heaviest group (>300 lbs or >136 kg) had the highest adjusted odds ratios (OR) for gestational diabetes (OR 5.2), preeclampsia (OR 5.0), and cesarean delivery (OR 2.7) compared with women weighing 100–149 lbs (45–67 kg). Compared with the reference group, the heaviest women were more likely to have a macrosomic infant and an infant treated in the NICU (OR 4.2 and 1.9, respectively). Even among a subsample of women who did not have any diabetic or hypertensive diseases, excess weight significantly increased the likelihood of macrosomia and NICU treatment. Blacks were disproportionately represented in the two heaviest groups (49.8% of those weighing 200–299 lbs and 63.9% of those weighing over 300 lbs).
CONCLUSION: In this population-based study of pregnant women, the adverse outcomes associated with excessive weight underline the urgency of weight loss interventions before pregnancy. The analysis also suggests that research is needed on rapidly growing racial or ethnic subgroups most at risk for obesity.
The prevalence of obesity in the United States is increasing rapidly, with corresponding increases in the risks for diabetes, heart disease, stroke, and cancer.1,2 In women of childbearing age, overweight and obesity have been associated with particular adverse effects, including greater risk of infertility, maternal morbidity, complications of labor and delivery, neural tube defects, and perinatal mortality.3–5 Among pregnant women, higher weights have been associated with gestational diabetes, preeclampsia, eclampsia, cesarean delivery, and infant macrosomia.6–11 There is evidence that the obesity-related risks during pregnancy vary by race, with obese Hispanic and black women more likely to have adverse outcomes than obese white women.11
In this study we analyzed the New York City birth files, a large database with a diverse population and with large numbers of overweight or obese women. Unlike earlier studies that examined births at a single hospital,12 this study has the advantage of utilizing population-based data. Although these files may have some limitations related to differences in reporting from provider to provider, from hospital to hospital, and from recall biases, they provide a rich source of information for highlighting the associations between excessive maternal weight and adverse outcomes for both women and infants.
We focused on women weighing 200 lbs (91 kg) or more before pregnancy, who are generally assumed to be at greatest risk for complications, including those associated with cesarean delivery, but about whom there is little information.13 Understanding the relationship between maternal obesity and perinatal outcomes is necessary in order to develop programs of preconception planning and weight control. This issue is of increasing clinical and public health import as the proportion of women who are overweight and obese is rapidly increasing.
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MATERIALS AND METHODS |
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Since the birth file does not contain data on the mother’s height we could not compute body mass index; therefore, we used mother’s prepregnancy weight as the measure of overweight and obesity. We constructed the following five categories of prepregnancy weight: 99 lbs or less (45 kg), 100–149 lbs (45–67 kg), 150–199 lbs (68–90 kg), 200–299 lbs (91–135 kg), and at least 300 lbs (136 kg). We feel confident that classifying women in the top two categories as overweight or obese is reasonable because a weight of 200 lbs corresponds to a body mass index of 29 for a woman whose height is 5'10''and a weight of 300 corresponds to a body mass index of 43 for a woman whose height is 5'10''.
Women with prepregnancy weights of 100–149 lbs were chosen as the reference group because they were the modal group (n = 135,925). The bivariate associations between maternal prepregnancy weight and the outcome variables were first evaluated using 
2 tests. Multiple logistic regressions were then performed with the same outcomes—gestational diabetes, preeclampsia, cesarean delivery, very low birthweight (VLBW) infant (under 1500 g [3.3 lbs]), macrosomic infant (4000 g [8.8 lbs] or more), and infant admission to the neonatal intensive care unit (NICU). (There were no data pertaining to shoulder dystocia or brachial plexus injury secondary to macrosomia.) Statistical adjustment was made for the following confounders: mother’s age, race or ethnicity, marital status, education, parity, social risk (eg, smoking), timing of prenatal care initiation, prenatal care payer, and infant’s sex.
Because obesity contributes to various chronic diseases, we performed similar regression analyses on a subsample of women without any of the six most commonly occurring chronic diseases of reproductive aged women, ie, chronic diabetes, gestational diabetes, chronic high blood pressure, pregnancy-related high blood pressure, preeclampsia, and eclampsia, in order to assess whether obesity was independently associated with adverse perinatal outcomes. SPSS 9.0 for Windows was used for data analysis (SPSS Inc., Chicago, IL).
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RESULTS |
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shows that almost all of the demographic characteristics and risk factors during pregnancy varied significantly by prepregnancy weight group (by 2 tests). Women in the two heaviest weight groups (200–299 lbs and >300 lbs) were most likely to be older, black, unmarried, have a high school degree or some college, have had previous live births, and to have smoked, drunk alcohol, or used an illegal drug during pregnancy. The most striking of these differences was that whereas black women comprised 27.6% of the entire sample, they accounted for 49.8% and 63.9% of the two heaviest weight categories. There were similar numbers of very small and very large infants: 2659 (1.2%) weighed 1500 grams or less and 2615 (1.2%) weighed 4500 grams or more.
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). Compared with the reference group, women weighing 200–299 lbs were four times more likely to have gestational diabetes, nearly three times more likely to have preeclampsia, and twice as likely to have a cesarean delivery. The heaviest weight group (>300 lbs) was five times as likely as the reference group to have gestational diabetes or preeclampsia and more than 2.5 times as likely to have a cesarean. It is worth noting that for women weighing 200 lbs or more compared with those weighing less than 200 lbs, a prior cesarean delivery was more often cited as an indication for the current cesarean delivery (33.1% compared to 27.2%, P < .001). However, for heavier women it was less likely for the record to show other indications for a cesarean delivery, eg, failure to progress (29.7% for the heavier women and 32.4% for the women under 200 lbs, P < .001).
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The relationship between prepregnancy weight and VLBW infant differed from the patterns shown with other outcomes (Table 3). In both the full sample and the subsample, the leanest mothers (
99 lbs) and mothers weighing 150–299 lbs were at greater risk of having a VLBW infant than were the reference group; mothers weighing 300 lbs and over were at reduced risk. There was, however, a consistent association between prepregnancy weight and macrosomia, with higher odds ratios corresponding with higher maternal weights. Mothers weighing 200–299 lbs were three times more likely to have a macrosomic infant than the reference group, and mothers weighing over 300 lbs were nearly four times more likely to have a macrosomic infant, for both the entire sample and the subsample of women without diabetic or hypertensive conditions.
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). For both the full sample and the subsample, women in the heaviest weight group were at higher risk of having an infant in the NICU (OR 1.9 and 1.5, respectively). This pattern of increased risk with higher maternal weight, however, did not hold true for the subsample of healthy mothers. However, a high percentage of the heaviest women were eliminated from the subsample; 28% of the women weighing over 300 lbs were excluded from the subsample analysis because they had at least one of the six diseases. In a separate analysis, we found that 20% of women weighing 200 lbs or more before pregnancy gained between 26 and 35 lbs during pregnancy, and over 25% gained more than 35 lbs during pregnancy, far greater gains than the Institute of Medicine recommendation of 15–25 lbs for overweight women. We also found that many women who weighed less than 200 lbs before pregnancy moved into the 200 and over category by delivery. Ten percent of the black women who weighed less than 174 lbs before pregnancy weighed more than 200 lbs at delivery.
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DISCUSSION |
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The birth certificate data do not permit examination of the postpartum course of women who gave birth in New York City, but the high rates of cesarean delivery in women weighing 200–299 lbs (33.3%) and women weighing 300 lbs or more (40.5%) are of concern. The postoperative complications of cesarean delivery, including infection (eg, endometritis), operative injury, need for transfusion, thromboembolism, and hysterectomy, are likely to be more frequent in immobile obese women. Morbidly obese women also have significantly longer postpartum hospital confinement.6–9,12,14
The association between overweight and cesarean rate might reflect regional variations in obstetric practices. A study conducted in a midwestern city found that obese women were more likely to have cesarean deliveries but at a much lower rate (7.7%)9 than those found for the women in the heaviest weight categories in New York City.
In this large urban sample, black women were much more likely to be obese than others. This confirms the recent analysis of National Health and Nutrition Examination Survey data, which found that non-Hispanic black women aged 20–39 years, ie, those of peak childbearing age, are significantly more likely to be overweight (70.8% had a body mass index over 25) and obese (46.2% had a body mass index over 30) than non-Hispanic whites.1 Another study of black women in New York City found that weight gain during pregnancy was highest for women who were overweight or obese before pregnancy and that these women were on average 20 lbs over their prepregnancy weight at both 2 months and 6 months postpartum.15 Weight gain during pregnancy, therefore, put these women at heightened risk of excessive weight before the next pregnancy.16
New York City is more diverse than the nation (25.9% versus 14.7% of all births were to blacks; 32.4% versus 21.7% of all births were to Hispanics), with a high concentration of risk among women delivering (44.1% of births were to unmarried women compared with 33.8%; the rate of low birth weight in New York City was 8.5% versus 7.8%).17,18 However, the population size and diversity of New York City both make the findings robust and enable us to learn quickly about population level trends and emerging public health problems. Although these associations may have been noted on an individual clinical level, a study such as this highlights that obesity has become a significant perinatal public health risk.
The vital statistics files used for this study are known to have limitations, including uneven and invalid reporting. An earlier study of the completeness of New York City birth certificate data, however, suggested that because the city is the only municipality in the country recording its own vital data, it has a superior degree of supervision and consistency in the reporting process across hospitals (Higginson G, Internal Memo, New York City Department of Health, Bureau of Maternity Services and Family Planning, 1982). Another study found that the mother’s report of prepregnancy weight was consistent with the actual clinical record data.19 Unfortunately, there are no similar studies that evaluated the accuracy of all the variables that were used in this analysis. A final limitation of our analysis is that we examined only live births, so we were not able to measure the association between prepregnancy weight and spontaneous abortion or fetal demise.
Recent studies have raised concerns about other negative outcomes related to maternal obesity. In one study, obesity before pregnancy was associated with a lower rate of breastfeeding initiation and a shorter period of breastfeeding.20 In another cohort study of women followed up into older age, women who developed hypertensive diseases during pregnancy were more likely to develop hypertension and stroke later in life.21
Finally, our results and those of previous studies suggest that all clinicians provide ongoing counseling about the risks of overweight and obesity to women in the childbearing years.6,7,15,22 We agree with the suggestion, in a recent study of maternal weight and high birth weight infants, that counseling and help with weight loss should occur before pregnancy23 because there are inadequate data about the effects of weight loss during the prenatal and immediate postpartum periods. Health practitioners should also be concerned about excessive weight gain during pregnancy (above the Institute of Medicine’s recommendations), which is related to adverse outcomes. Because weight loss is difficult to achieve and maintain, it underscores the necessity for clinicians to have a long-term view of weight, nutrition, and exercise as a lifetime concern and not just one restricted to pregnancy.
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Footnotes |
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Received May 15, 2003. Received in revised form July 16, 2003. Accepted July 23, 2003.
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REFERENCES |
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2. Weisberg S. Societal change to prevent obesity. JAMA 2002;288:2176.
3. Cnattingius S, Bergstrom R, Lipworth L, Kramer MS. Prepregnancy weight and the risk of adverse pregnancy outcomes. N Engl J Med 1998;338:147–52.
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16. Rooney BL, Schauberger CW. Excess pregnancy weight gain and long-term obesity: One decade later. Obstet Gynecol 2002;100:245–52.
17. Hamilton BE, Martin JA, Sutton PD. Births: Preliminary data for 2002. National vital statistics reports. Vol 51, no 11. Hyattsville, Maryland: National Center for Health Statistics, 2003.
18. Schwartz S, Li W. Summary of vital statistics 2001: The City of New York. New York City Department of Health and Mental Hygiene. New York: Bureau of Vital Statistics, 2003.
19. Lederman SA, Paxton A. Maternal reporting of prepregnancy weight and birth outcome: Consistency and completeness compared with the clinical record. Matern Child Health J 1998;2:123–6.[Medline]
20. Li R, Jewell S, Grummer-Strawn L. Maternal obesity and breast-feeding practices. Am J Clin Nutr 2003;77: 931–6.
21. Wilson BJ, Watson MS, Prescott GJ, Sunderland S, Campbell DM, Hannaford P, et al. Hypertensive diseases of pregnancy and risk of hypertension and stroke in later life: Results from cohort study. BMJ 2003;326:8–15.
22. Serdula MK, Khan LK, Dietz WH. Weight loss counseling revisited. JAMA 2003;289:1747–50.
23. Orskou J, Henriksen TB, Kesmodel UK, Secher NJ. Maternal characteristics and lifestyle factors and the risk of delivering high birth weight infants. Obstet Gynecol 2003; 102:115–20.
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