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

Objective: To determine the accuracy of ultrasonography for predicting a large-for-gestational-age (LGA) newborn in women with gestational diabetes mellitus (GDM).Materials and Methods: Singleton pregnancy, diagnosed with GDM were recruited. They underwent ultrasonography at 32-36 weeks’ gestation for fetal biometry. 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.Results: Of 345 studied women, 107 (31%) had an LGA newborn. EFW of ≥ 90 th 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 > 90 th percentile and HC > 90 th 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 > 85 th percentile had the highest OR of 9.3 (1.1-77.9). Lowering cutoff values of EFW to 80 th and 70 th 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 GDM had high PPV and specificity with low to moderate sensitivity and NPV to predict an LGA newborn in GDM.