The clinical utility of oral glucose tolerance test at term: can it predict fetal macrosomia?

Objective: The goal of this study was to assess the correlation between true fetal macrosomia and abnormal oral glucose tolerance test (OGTT) in pregnant women at term gestation who had a negative glucose challenge screen (GCT) at 24-28 weeks.
Study Design: In this cohort observational study, we enrolled all term pregnant patients who presented to our antenatal unit with estimated fetal weight >90th percentile (or >4,000 g) and negative 50 g GCT. The women underwent a 3-h (100 g) OGTT test. Patient's demographics, GCT and OGTT test results, mode of delivery and pregnancy outcomes were recorded and analyzed.
Results: One hundred and seventy women (mean age 30.2+4.6 years, range 19-44) were recruited over 15-month period. Ten patients (5.9%) were identified as having impaired glucose metabolism at term. In this sub-group, we found no correlation between GCT values at 24-28 weeks, family history of diabetes mellitus, the patient's BMI or weight at term, and the diagnosis of impaired glucose metabolism. There was no statistically significant difference in the mean fetal weight in patients with normal and abnormal OGTT. No shoulder dystocia or third and fourth degree vaginal tears were reported among the women with suspected fetal macrosomia and impaired glucose metabolism.
Conclusions: There was no correlation between true fetal macrosomia and an abnormal 3-h (100 g) OGTT at term. A larger-scale study is needed to determine the clinical significance of performing an OGTT at term for all patients with macrosomia and negative gestational diabetes screen.