Quantifying the impact of gestational diabetes mellitus, maternal weight and race on birthweight via quantile regression

Abstract

Background: Quantile regression, a robust semi-parametric approach, was used to examine the impact of gestational diabetes mellitus (GDM) across birthweight quantiles with a focus on maternal prepregnancy body mass index (BMI) and gestational weight gain (GWG).

Methods: Using linked birth certificate, inpatient hospital and prenatal claims data we examined live singleton births to non-Hispanic white (NHW, 135,119) and non-Hispanic black (NHB, 76,675) women in South Carolina who delivered 28-44 weeks gestation in 2004-2008.

Results: At a maternal BMI of 30 kg/m² at the 90(th) quantile of birthweight, exposure to GDM was associated with birthweights 84 grams (95% CI 57, 112) higher in NHW and 132 grams (95% CI: 104, 161) higher in NHB. Results at the 50(th) quantile were 34 grams (95% CI: 17, 51) and 78 grams (95% CI: 56, 100), respectively. At a maternal GWG of 13.5 kg at the 90(th) quantile of birthweight, exposure to GDM was associated with birthweights 83 grams (95% CI: 57, 109) higher in NHW and 135 grams (95% CI: 103, 167) higher in NHB. Results at the 50(th) quantile were 55 grams (95% CI: 40, 71) and 69 grams (95% CI: 46, 92), respectively.

Summary: Our findings indicate that GDM, maternal prepregnancy BMI and GWG increase birthweight more in NHW and NHB infants who are already at the greatest risk of macrosomia or being large for gestational age (LGA), that is those at the 90(th) rather than the median of the birthweight distribution.

Figure 1. Flow chart defining study population and exclusions.

Figure 2. Predicted Infant Birthweight using model 1.

Results pictured for mother’s age 26, gestational age 38 weeks, 11.3 kg (25 lbs) weight gain, averaged over effects of infant sex, prenatal care, smoking, hypertension, first born, and availability of prenatal information at the 50^th (A), 75^th (B), and 90^th (C) quantile.

Figure 3. Predicted Infant Birthweight using model 2.

Results pictured for mother’s age 26, gestational age 38 weeks, prepregnancy BMI 30, averaged over effects of infant sex, prenatal care, smoking, hypertension, first born, and availability of prenatal information at the 50^th (A), 75^th (B), and 90^th (C) quantile.

Figure 4. Effect of GDM on Birthweight by Quantile.

Effect of GDM on birthweight in Model One (A) and Model Two (B). The figure presents the additional birthweight associated with a mother having GDM in NHW and NHB for a maternal BMI of 30 or 35 (A) or gestational weight gain of 13.5 or 18 kg (B).