Maternal pre-pregnancy weight and gestational weight gain and their association with birthweight with a focus on racial differences

Abstract

Our objectives were to examine the interaction between maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) and their association with birthweight, with a focus on racial differences. We used birth certificate data from live singleton births of South Carolina resident mothers, who self-reported their race as non-Hispanic white (NHW, n = 140, 128) or non-Hispanic black (NHB, n = 82,492) and who delivered at 34-44 weeks of gestation between 2004 and 2008 to conduct a cross-sectional study. Linear regression was used to examine the relationship between our exposures (i.e., race, BMI and GWG) and our outcome birthweight. Based on 2009 Institute of Medicine guidelines, the prevalence of adequate, inadequate and excessive GWG was 27.1, 24.2 and 48.7%, respectively, in NHW women and 24.2, 34.8 and 41.0%, respectively, in NHB women. Adjusting for infant sex, gestational age, maternal age, tobacco use, education, prenatal care, and Medicaid, the difference in birthweight between excessive and adequate GWG at a maternal BMI of 30 kg/m(2) was 118 g (95% CI: 109, 127) in NHW women and 101 g (95% CI: 91, 111) in NHB women. Moreover, excessive versus adequate GWG conveyed similar protection from having a small for gestational age infant in NHW [OR = 0.64 (95% CI 0.61, 0.67)] and NHB women [OR = 0.68 (95% CI: 0.65, 0.72)]. In conclusion, we report a strong association between excessive GWG and higher infant birthweight across maternal BMI classes in NHW and NHB women. Given the high prevalence of excessive GWG even a small increase in birthweight may have considerable implications at the population level.

Figure 1

Flow chart defining study population and exclusions.

Figure 2

Histograms of gestational weight gain in NHW and NHB women stratified by pre-pregnancy BMI category. According to Institute of Medicine, recommended gestational weight gain (GWG) is defined as 25 to 35 pounds (11.34 to 15.88 kg) for women with normal BMI, 15 to 25 pounds (6.80 to 11.34 kg) for overweight women and 11 to 20 pounds (4.99 to 9.07 kg) for obese women

Figure 3

Birthweight curves specific to gestational weight gain (GWG) stratified by maternal race and maternal pre-pregnancy BMI category. The linear regression model used included maternal age, infant sex, race, maternal tobacco use, maternal high school education, being first born, prenatal care as defined by the revised GINDEX, Medicaid status, four terms for gestational age (i.e., linear, quadratic, cubic and 4th order polynomial term), three terms for GWG (i.e., linear, quadratic and cubic), a categorical variable for maternal pre-pregnancy BMI category (i.e., normal weight, overweight and obese) and appropriate interaction terms between race, GWG and maternal pre-pregnancy BMI categories. Birthweight was the outcome of interest.

Figure 4

Birthweight curves specific to maternal pre-pregnancy BMI stratified by maternal race and gestational weight gain (GWG) category. The linear regression model used included maternal age, infant sex, race, maternal tobacco use, maternal high school education, being first born, prenatal care as defined by the revised GINDEX, Medicaid status, four terms for gestational age (i.e., linear, quadratic, cubic and 4th order polynomial term), two terms for maternal pre-pregnancy BMI (i.e., linear and quadratic) and a categorical variable for GWG (i.e., adequate, inadequate and excessive) and appropriate interaction terms between race, maternal pre-pregnancy BMI and GWG categories. Birthweight was the outcome of interest.