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

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-h threshold of ≤180 mg/dL, or 2-h threshold of ≤153 mg/dL are exceeded during the 75-g 2-h 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; however, 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. However, neither the JSOG nor the WHO has provided any evidence that it is appropriate to use a threshold beyond the range recommended by the IADPSG. 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 into 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: In total, the NGT and GDM group comprised 189 and 49 women, respectively. 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); however, 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). No significant differences were observed in other maternal and neonatal outcomes between both groups. CONCLUSION: Although a diagnosis of GDM during the third trimester does not improve pregnancy outcomes, it increases the elective caesarean delivery rate.