The importance of a postpartum 75 g oral glucose tolerance test in women with gestational diabetes.

OBJECTIVE To compare the ability of the fasting plasma glucose (FPG) level with the ability of the 2-hour oral glucose tolerance test (OGTT) to identify women with any form of glucose intolerance within the first six postpartum months. METHODS In a retrospective, observational analysis, the predictive ability of the FPG level was compared with that of the 2-hour OGTT in 275 women followed for gestational diabetes who returned for postpartum testing. RESULTS With use of the FPG level alone, 4.4% of the women were found to have an FPG 7.0 mmol/L, identifying diabetes mellitus (DM); 2.5% had an FPG in the range 6.1-6.9 mmol/L, identifying impaired fasting glucose (IFG); and 93% had an FPG 6.0 mmol/L, i.e., within the normal range. Using the 2-hour 75g OGTT, 5% of women were found to have either an FPG 7.0 mmol/L or a 2-hour plasma glucose (PG) 11.1 mmol/L, identifying DM; 2.5% had an FPG of 6.1-6.9 mmol/L, identifying IFG; and 32% had a 2-hour PG of 7.8-11.0 mmol/L, identifying impaired glucose tolerance (IGT). Of the women with any glucose abnormality postpartum, an FPG level alone detected 15.8%, the post-glucose load level detected 97.5%, and an OGTT detected 100% of the women. An FPG level alone in 39% of cases failed to detect either IGT or DM and in 54% of cases, type 2 DM. CONCLUSION In view of the potential for early, effective prevention of DM, the optimal method for detecting glucose abnormalities in women within six months post partum is a 2-hour OGTT.