Prediction of large for gestational age birth weights in diabetic mothers based on early third-trimester sonography

Objectives-The purpose of this study was to evaluate the ability of early third-trimester sonography to predict large for gestational age (LGA) birth weights in women with diabetes mellitus. Methods-We identified women with nonanomalous singleton gestations and pregestational and gestational diabetes mellitus who underwent sonographic examinations between gestational ages of 28 weeks and 32 weeks 6 days and subsequently delivered at 37 weeks or later. Using a cohort study design, we compared data from women with an estimated fetal weight at or above the 75th percentile (exposed group) with data from those with an estimated fetal weight below the 75th percentile (unexposed group). The primary outcome variable was LGA birth weight, defined as a birth weight of greater than 90% for gestational age. Results-Eighty-six women met inclusion criteria over a 3-year period: 40 were in the exposed group, and 46 were in the unexposed group. The mean body mass indices ± SD at delivery were similar for both groups: 35.4 ± 8.2 kg/m² exposed versus 35.0 ± 8.2 kg/m² unexposed (P = .80). There was no difference in the number of women with gestational diabetes mellitus: 40% exposed versus 39% unexposed (P = .90). Neonates whose early third-trimester estimated fetal weight was at or above the 75th percentile were significantly more likely to be LGA at birth compared with neonates whose early third-trimester estimated fetal weight was below the 75th percentile: 65% exposed versus 15% unexposed (P < .001; odds ratio, 10.3; 95% confidence interval, 3.7-29.1). There was no significant difference in cesarean delivery rates: 60% exposed versus 44% unexposed (P = .13) Conclusions-Measurements obtained by early third-trimester sonographic fetal biometry are reasonably predictive of fetal LGA birth weights at term.