Prepregnancy Obesity Trends Among Low-Income Women, United States, 1999–2008

Stefanie N. Hinkle; Andrea J. Sharma; Shin Y. Kim; Sohyun Park; Karen Dalenius; Patricia L. Brindley; Laurence M. Grummer-Strawn


Matern Child Health J. 2012;16(7):1339-1348. 

In This Article


In this study, we provide specific evidence that obesity is a public health problem among low-income women entering pregnancy, as the prevalence of obesity steadily increased from 1999 to 2008. Our data support prior studies, which indicate that obesity continues to increase in general among women of reproductive age[13] and among women entering pregnancy.[11] Prepregnancy obesity increased over the last decade such that the overall unadjusted prevalence increased from 24.8% in 1999 to 28.5% in 2008, a relative increase of 14.9% over 1999. Our data indicate that the increase in prepregnancy obesity among low-income women cannot solely be attributed to changes in maternal age and race-ethnicity in this population, as there was a 14.1% increase from 1999 when adjusted for these changes in demographics. In 2008, more than half of the women enrolled in WIC during pregnancy were overweight or obese prior to becoming pregnant. In addition, severe obesity is a concern, as almost half of the obese women were categorized as class II or III obese. We found that the obesity situation differs by contributor, which may represent a combination of the population served by WIC within each contributor, as well as the environment of each contributor.

Results from previous studies have shown that in the general population race-ethnicity is associated with obesity independently of income status.[19] We similarly found substantial racial-ethnic variations in the prevalence of prepregnancy obesity among low-income women in 2008. Among our study population of low-income, reproductive age women, racial and ethnic differences in the prevalence of obesity still exist. The prevalence of prepregnancy obesity was higher among non-Hispanic whites than among Hispanics, which conflicts with results of a study based on Pregnancy Risk Assessment Monitoring System (PRAMS) data[10] and a study based on National Health and Nutrition Examination Survey (NHANES) data;[13] however, neither study was limited to low-income women. Results from other studies have also suggested that the relationship between obesity and income status among women may differ by race-ethnicity.[20,21] In addition the prevalence of prepregnancy obesity among Hispanics enrolled in WIC is increasing rapidly. Additional studies are needed to further examine the race-ethnic differences in obesity specifically among low-income women of reproductive age.

Our finding that trends in prepregnancy obesity rates adjusted for women's age and race-ethnicity were almost identical to the unadjusted trends indicated that changes in the distribution of these characteristics among low-income women were not an important factor in the increase in obesity rates. However, in this population we observed competing effects of standardizing solely for age or solely for race-ethnicity, indicating that future researchers should consider similarly adjusting for both factors when evaluating trends in prepregnancy obesity among low-income women.

The high proportion of severely obese WIC participants is cause for concern both as the risk for adverse obstetric outcomes increases with increasing prepregnancy BMI[1] and because severe obesity is associated with increased risk for health problems later in life, including diabetes, cardiovascular disease, and cancer.[22] Given the risks involved, maternal obesity prevention before, during, and after pregnancy is vital. Preconception obesity prevention and treatment prior to women entering WIC are needed to improve health and obstetric outcomes among low-income women. The Institute of Medicine (IOM) recommends that women be in the normal weight range when they conceive and that preconception counseling include topics such as weight loss, diet, physical activity, and contraception.[23] Because financial barriers may prevent low-income women from receiving appropriate preconception care, the CDC has recommended strategies to increase public and private health insurance access to low-income women to increase preconception care.[24]

Weight loss prior to pregnancy is not always feasible given that many pregnancies are unplanned and losing weight is difficult.[25] Once pregnant, women should be counseled about the amount of gestational weight gain that is appropriate to help reduce pregnancy complications associated with obesity. Due to a lack of evidence concerning what constitutes an appropriate gestational weight gain for severely obese women, the current IOM gestational weight gain recommendations for obese women are not differentiated by obesity severity.[23] Some evidence, however, suggests that appropriate gestational weight gain for class II and III obese women may be lower than the current recommendation for all obese women.[26–28] Although health literacy among low-income women presents an additional challenge for interventions,[23] nevertheless when successful, limiting postpartum weight retention may help reduce women's risk for weight-related adverse outcomes during subsequent pregnancies. In addition, dietary and physical activity counseling during and after pregnancy has been shown to reduce postpartum weight retention among obese women.[23,29,30]

The PNSS provides census data on all low-income women who utilized WIC services during their pregnancy among the participating states, territories and Indian tribal organizations and may provide insight into the prepregnancy obesity situation among low-income women across various regions in the United States. However, our results may not be generalizable to all low-income pregnant women in the United States. First, not all states participate in the PNSS as it is a voluntary surveillance system. Second, not all eligible pregnant women utilize WIC services and utilization may differ by maternal characteristics or by state.[31] Also, during the study period, the number of women who participated in WIC increased, either because of an increase in utilization rates among eligible women or an increase in the number of women eligible for WIC services.[32] Although it is unclear how changes in the number of WIC participants may have affected our results, we adjusted our prevalence estimates to account for changes in maternal age and race-ethnicity distributions, indicating that the observed trends are independent of the demographic changes in the population. In addition, we could not examine how behavioral, environmental, or policy changes impacted the trends observed in our study.

The large size of our study sample allowed us to estimate prepregnancy obesity trends in specific racial-ethnic groups, including American Indians/Alaskan Natives and Asians/Pacific Islanders, groups often excluded from analyses because of their relatively small numbers. We were unable to include Hawaii in our analyses because of the high proportion of women who classified themselves as multiracial. Previous studies of racial-ethnic variations in obesity prevalence among Hawaiian women have shown the prevalence to be highest among Native Hawaiians.[33,34]

We also provide prepregnancy obesity trends by obesity class, where little data among women becoming pregnant are currently available. Most previous research concerning obesity among pregnant women has focused on class I obese women;[23] however, we found that almost half of obese low-income women were class II or class III obese. In addition, because our prepregnancy BMI estimates were based on maternal self-reports of prepregnancy weight and women often report weighing less than their true weight,[35] the prevalence of prepregnancy obesity among low-income women may be even higher than we estimated; although, the use of measured maternal height may help to minimize the bias in our BMI estimates compared to studies of self-reported height and weight.

In conclusion, our findings indicate that prepregnancy obesity remains a critical issue for low-income women. Overall the prevalence of prepregnancy obesity increased steadily among low-income women from 1999 to 2008. Similarly the proportion of women who were normal weight prior to pregnancy decreased, such that in 2008 only 41.1% of the women in this population were at a normal weight prior to pregnancy, indicating that none of the contributors met the Healthy People 2020 target of 53.4% of women entering pregnancy at a normal weight.[36] Obesity prevention programs targeting low-income women of reproductive age may be an important strategy to decrease the burden of obesity on maternal and child health.