Third trimester re-screening for gestational diabetes in morbidly obese women despite earlier negative test can reveal risks for obstetrical complications.

Aim: We investigated associations of maternal obesity with late gestational diabetes mellitus (GDM) diagnosis (>34 weeks) in women with previous normal glucose screening, and associations of late GDM with obstetrical outcomes.

Methods: This retrospective cohort study assessed obstetrical and neonatal outcomes of 238 women with normal (24-28 week) glucose screening results, who underwent late repeat oral glucose tolerance tests (OGTT) (>34 weeks) due to a suspected LGA fetus (54.6%) or polyhydramnios (45.4%). A sub-analysis was performed of outcomes of women with late versus mid-trimester GDM.

Results: The GDM rate in repeat OGTT screening was 22.2% for the total sample, and 33% among women with morbid obesity. Among women with late GDM versus without late GDM, rates were higher for macrosomia, large-for-gestational-age fetus induction of labor, neonatal hypoglycemia, jaundice, and the need for phototherapy. Among women with late GDM, a higher pregestational BMI was associated with adverse maternal and perinatal outcomes. Higher risks for macrosomia and CS due to macrosomia were demonstrated in women with late vs. mid-trimester GDM.

Conclusion: Late screening in pregnancy may reveal GDM among women with previous normal glucose screening, particularly among those with late third trimester BMI ≥ 35 kg/m , GDM in a previous pregnancy or fasting glucose >95 mg/dl. Women diagnosed with GDM at >34 weeks following normal glucose screening at 24-28 weeks are at higher risk for adverse perinatal outcomes. For women with morbid obesity, or suspected macrosomia or polyhydramnios in the late third trimester, and normal glucose screening in the second trimester, retesting should be considered.