Impact of gestational diabetes mellitus diagnosed during the third trimester on pregnancy outcomes: A case control study

Abstract

Background: In 2010, the International Association of Diabetes and Pregnancy Study Group (IADPSG) proposed new criteria indicating that gestational diabetes mellitus (GDM) can be diagnosed if the fasting threshold of ≤92 mg/dL, 1-hour threshold of ≤180 mg/dL, or 2-hour threshold of ≤153 mg/dL are exceeded during the 75-g 2-hour oral glucose tolerance test (OGTT) performed at 24–28 weeks of gestation. The World Health Organization (WHO) recommends using the proposed diagnostic threshold values of the IADPSG to diagnose GDM, but it does not limit the timing of the 75-g OGTT. Since 2010 in Japan, GDM has been diagnosed using the same criteria as that proposed by the WHO. Nevertheless, there is no justification for these thresholds during specific time windows.Methods: This was a single-centre retrospective study based on the medical records and delivery registry database of our centre. We included women who underwent a 50-g glucose challenge test (GCT) with results <140 mg/dL at 24–28 weeks of gestation and subsequently underwent a 75-g OGTT after 29 weeks of gestation with abnormal glucose tolerance suspected based on clinical findings. The reference values for the 75-g OGTT followed the IADPSG criteria. Subjects were classified as the normal glucose tolerance (NGT) group and the GDM group. The type of delivery and neonatal outcomes of the two groups were compared. A multivariable analysis was performed to match the backgrounds of both groups.Results: A total of 189 women comprised the NGT group and 49 women comprised the GDM group. Emergency caesarean delivery rates were similar in the GDM and NGT groups (10.6% and 12.2%, respectively; adjusted odds ratio [OR], 1.25; 95% confidence interval [CI], 0.43-3.64; p=0.74), but the elective caesarean delivery rate was higher in the GDM group than in the NGT group (16.3% and 5.3%, respectively, adjusted OR, 3.60; 95% CI, 1.27-10.19; p=0.01). There were no differences in other maternal and neonatal outcomes between groups.Conclusion: Whether diagnosing GDM during the third trimester can improve pregnancy outcomes is unknown. However, pregnant women diagnosed with GDM during the third trimester are more likely to undergo caesarean delivery.