Indications for the Postpartum Oral Glucose Tolerance Test.

Background: Gestational diabetes mellitus (GDM) affects more than 50 000 pregnant women in Germany every year. In postpartum diabetes screening, a 75 g oral glucose tolerance test (OGT) is recommended. This is time-consuming and can have side effects, and only 40% of mothers take it. The determination of pre-test probabilities might obviate the need for OGT except in women who are at particular risk.

Methods: We analyzed 5444 cases of GDM from the GestDiab registry over the period 2015-2019. The pretest probabilities of a postpartum diagnosis of diabetes mellitus (DM) or prediabetes were calculated on the basis of clinical variables including postpartum venous fasting plasma glucose (FPG) and hemoglobin A1c (HbA1c).

Results: In 0.77% of mothers with a history of GDM in whom DM was not detected by FPG or HbA1c, postpartum DM was diagnosed on the basis of the 2-hour value in the OGT. Individual estimation of the pre-test probability of a diagnosis by OGT of postpartum DM or prediabetes was possible with the aid of the FPG and HbA1c values and clinical predictors including insulin treatment during pregnancy, obesity, GDM diagnosed before 24 weeks of gestation, age over 35, and a 1-hour value in the diagnostic OGT during pregnancy of 180 mg/dL (10.0 mmol/L) or above. The pretest probability of postpartum DM in the study group ranged from 0.11% to 4.17%, and that of postpartum prediabetes from 6.4% to 16.3%.

Conclusion: The probability of a diagnosis of postpartum diabetes by OGT after GDM can be estimated in postpartum screening on the basis of various parameters. This enables risk-adapted counseling of the affected women along with a long-term strategy for diabetes prevention and follow-up. The findings of our study should be verified by further research.