Does the availability of maternal HbA1c results improve the accuracy of sonographic diagnosis of macrosomia?

Objective: To determine whether measuring maternal glycosylated hemoglobin (HbA1c) can improve the accuracy of sonographic estimation of fetal macrosomia. Methods: Sonographic estimation of fetal weight (EFW) and maternal HbA1c were obtained in term, non-diabetic patients within 1 week before delivery. Neonatal birth weights were recorded at delivery and compared with both sonographic estimations and HbA1c. Macrosomia was defined as birth weight of ≥ 4000 g. The absolute error of the sonographic EFW was calculated. Receiver-operating characteristics (ROC) curve analysis was used to evaluate sonographic EFW and HbA1c as predictors of birth weight ≥ 4000 g. Variables were tested using regression analysis and student's t-test. Results: One hundred and sixty two patients were evaluated between July and December 2002. Twenty-eight patients (17.3%) delivered macrosomic infants. Sonographic EFW ≥ 4000 g predicted macrosomia with sensitivity, specificity and positive and negative predictive values of 66.6%, 88.8%, 54.5% and 93.0%, respectively. Its overall accuracy was 85.5%. The area under the ROC curve of sonographic EFW in the prediction of macrosomia was 0.9 (P < 0.001). HbA1c levels in women delivering macrosomic and non-macrosomic neonates were 5.3 ± 0.7% and5.2 ± 0.5%, respectively (P = 0.27). The area under the ROC curve of HbA1c in the prediction of macrosomia was 0.53 (P = 0.27). Conclusions: Maternal HbA1c is not a useful test in the prediction of birth weight. It therefore cannot be used to improve the accuracy of sonographic EFW.