A majority of women in the United States with gestational diabetes mellitus do not undergo the recommended 4- to 12-week postpartum glucose tolerance test.

This study aimed to compare the diagnostic value of the 2-day postpartum glucose tolerance test with the 4- to 12-week postpartum glucose tolerance test to identify impaired glucose metabolism at 1 year after delivery among women with gestational diabetes.

Postpartum women who delivered at 1 hospital between January 2017 and July 2018 were offered enrollment in a prospective cohort if they had gestational diabetes mellitus diagnosed by Carpenter-Coustan criteria or a 1-hour glucose challenge test result of ≥200 mg/dL, spoke English or Spanish, and planned to remain in the hospital for at least 2 days after delivery. Participating women underwent a 75-gram 2-hour glucose tolerance test on postpartum day 2 and were incentivized to have a 4- to 12-week glucose tolerance test and measurement of glycosylated hemoglobin at 1 year after delivery. Participants and providers were blinded to the 2-day postpartum results. The diagnostic value of an abnormal 2-day postpartum glucose tolerance test (fasting result of ≥100 mg/dL or 2-hour glucose tolerance test result of ≥140 mg/dL) was compared with that of an abnormal 4- to 12-week glucose tolerance test to identify impaired glucose metabolism (≥5.7% glycosylated hemoglobin) and diabetes (≥6.5% glycosylated hemoglobin) at 1 year after delivery. Receiver operating characteristic (ROC) curves were also compared at 2 days and 4–12 weeks after delivery.

Of the 300 recruited women, 296 (99%) completed the 2-day postpartum glucose tolerance test, and 202 (68%) returned for the 4- to 12-week glucose tolerance test. Approximately 1 year after delivery, 203 (68%) women had their glycosylated hemoglobin measured, of whom 35% had impaired glucose metabolism and 4% had diabetes. The study population was diverse (46% nonwhite). Furthermore, 56% were obese (mean body mass index, 32 kg/m ² ), and 55% had received medication to control their glucose during pregnancy. There were no significant differences between the 2-day and 4- to 12-week postpartum glucose tolerance tests in predicting impaired glucose metabolism based on ≥5.7% glycosylated hemoglobin in 1 year after delivery: sensitivity (46% vs 36%); specificity (79% vs 84%); positive predictive value (52% vs 53%); and negative predictive value (75% vs 72%). There was also no difference between the 2-day and the 4- to 12-week glucose tolerance tests in identifying diabetes at 1 year after delivery. Both the 2-day and 4- to 12-week glucose tolerance tests had similar ROC curves in identifying impaired glucose metabolism and diabetes at 1 year after delivery.

Two-day postpartum glucose tolerance tests have similar diagnostic value as 4- to 12-week postpartum glucose tolerance tests in predicting impaired glucose metabolism and diabetes at 1 year after delivery and are associated with nearly 100% adherence to the test. Thus, changing the timing of the glucose tolerance test should be considered.