Screening for gestational diabetes. Optimum timing and criteria for retesting.

Because of the morbidity associated with undiagnosed gestational diabetes (GDM), screening programs are advocated in all pregnancy clinics. The purpose of this study was to elucidate the optimum time to test for diabetes during gestation, the indication for retesting, and the predictive value of a positive screening test for a large (greater than 4000 g) infant. Women (N = 300) were screened at three time points: 9-20 wk, 27-31 wk, and 33-36 wk. An additional group of 300 women were screened at two time points: 27-31 wk and 33-36 wk. The prevalence of GDM in this group was 3.2%. The optimum timing for screening for highest yield was 27-31 wk. Retesting at 33-36 wk appeared cost effective if (1) maternal age was greater than or equal to 33 yr, (2) a positive screen was present at 27-31 wk, and (3) the mother was obese (greater than 120% ideal body wt).