Accuracy of Third Trimester Ultrasound for Predicting Large-for-Gestational Age Newborn in Women with Gestational Diabetes Mellitus

Abstract

Objective: To determine the accuracy of ultrasonography during 32-36 weeks of gestation for predicting a largefor- gestational-age (LGA) newborn in women with gestational diabetes mellitus (GDM). Materials and Methods: Women with singleton pregnancy, aged ≥ 18 years old and diagnosed with GDM were recruited. They underwent ultrasonography at 32-36 weeks’ gestation for fetal biometry, namely, biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL). Estimated fetal weight (EFW) was derived from these 4 parameters by Hadlock formula. Delivery of an LGA newborn in women with the ultrasound finding of LGA fetus was the primary outcome of interest along with determination of predicting factors. Results: Of 345 studied women, 107 (31%) had an LGA newborn. EFW of ≥ 90th percentile at third trimester ultrasonography was found in 13 women, all of whom had an LGA newborn. It had a positive predictive value (PPV), specificity, sensitivity and negative predictive value (NPV) of 100%, 100%, 12.1% and 71.7% respectively to predict LGA at birth. Considering each fetal parameter individually, AC ≥ 90th percentile and HC ≥ 90th percentile had odds ratios (OR) with 95% confidence intervals of the newborn being LGA of 6.5 (3.3-12.8) and 2.0 (1.0-4.0) respectively while EFW ≥ 85th percentile had the highest OR of 9.3 (1.1-77.9). Lowering cutoff values of EFW to 80th and 70th percentile increased the sensitivity and NPV for prediction of LGA at birth while reducing the PPV and specificity slightly. Conclusion: EFW derived from the third trimester ultrasonography in women with GDM had high PPV and specificity with low to moderate sensitivity and NPV to predict an LGA newborn in women with GDM.