Oral glucose tolerance test results in early pregnancy: A Finnish population-based cohort study

To analyze early-pregnancy oral glucose tolerance test (OGTT) results and differences between early- and late-pregnancy OGTT results in a population-based cohort.

From 3/2013 to 12/2016, pregnant women in South Karelia, Finland, were invited to undergo a 2-hour 75 g OGTT at 12-16 weeks' gestation (OGTT1) and, if normal, repeat testing at 24-28 weeks (OGTT2). Early and late gestational diabetes (GDM) were diagnosed using the same nationally endorsed criteria (fasting [FPG], 1- or 2-hour plasma glucose ≥5.3, ≥10.0 or ≥8.6 mmol/L, respectively).

In OGTT1 (n = 1401), the mean (SD) FPG, 1- and 2-hour values were 4.85 (0.34), 6.63 (1.73) and 5.60 (1.28) mmol/L, respectively. Early GDM was diagnosed in 209 (14.9%). In OGTT2 (n = 1067), late GDM was diagnosed in 114 (10.6%). In women without GDM (n = 953), the mean FPG values were higher and post-load values lower in OGTT1 vs. OGTT2. No interaction effects of gestational timepoint and maternal BMI on OGTT results were detected, except for the 2-hour value. In women with late GDM, both mean FPG and post-load values were lower in OGTT1 vs. OGTT2. Results were similar employing the IADPSG GDM criteria.

Our findings suggest that gestational-age specific OGTT thresholds for early GDM diagnosis need to be generated.