Determinants of fetal growth at different periods of pregnancies complicated by gestational diabetes mellitus or impaired glucose tolerance.

OBJECTIVE To determine maternal parameters with the strongest influence on fetal growth in different periods of pregnancies complicated by an abnormal glucose tolerance test (GTT). RESEARCH DESIGN AND METHODS Retrospective study of 368 women with gestational diabetes mellitus (GDM; > or = 2 abnormal GTT values, n = 280) and impaired glucose tolerance (IGT; one abnormal value, n = 88) with 869 ultrasound examinations at entry to and during diabetic care. Both groups were managed comparably. Abdominal circumference (AC) > or = 90th percentile defined fetal macrosomia. Maternal historical and clinical parameters, and diagnostic and glycemic values of glucose profiles divided into five categories of 4 weeks of gestational age (GA; <24 weeks, 24 weeks/0 days to 27 weeks/6 days, 28/0-31/6, 32/0-35/6, and 36/0-40/0 [referred to as <24 GA, 24 GA, 28 GA, 32 GA, and 36 GA categories, respectively]) were tested by univariate and multiple logistic regression analysis for their ability to predict an AC > or = 90th percentile at each GA group and large-for-gestational-age (LGA) newborn. Data obtained at entry were also analyzed separately irrespective of the GA. RESULTS Maternal weight, glycemia after therapy, rates of fetal macrosomia, and LGA were not significantly different between GDM and IGT; thus, both groups were analyzed together. LGA in a previous pregnancy, (odds ratio [OR] 3.6; 95% CI 1.8-7.3) and prepregnancy obesity (BMI > or = 30 kg/m(2); 2.1; 1.2-3.7) independently predicted AC > or = 90th percentile at entry. When data for each GA category were analyzed, no predictors were found for <24 GA. Independent predictors for each subsequent GA category were as follows: at 24 GA, LGA history (OR 9.8); at 28 GA, LGA history (OR 4.2), and obesity (OR 3.3); at 32 GA, fasting glucose of 32 GA (OR 1.6 per 5-mg/dl increase); at 36 GA, fasting glucose of 32 GA (OR 1.6); and for LGA at birth, LGA history (OR 2.7), and obesity (OR 2.4). CONCLUSIONS In the late second and early third trimester, maternal BMI and LGA in a previous pregnancy appear to have the strongest influence on fetal growth, while later in the third trimester coincident with the period of maximum growth described in diabetic pregnancies, maternal glycemia predominates.