Gestational diabetes: Is a 50-g screening result ≥ 200 mg/dL diagnostic?

OBJECTIVE: To evaluate the diagnosis of gestational diabetes based on a 50-g, one-hour glucose screening test result ≥ 200 mg/dL. STUDY DESIGN: Retrospective ascertainment of pregnant women who had a 50-g, one-hour glucose screening test result ≥200 mg/dL was performed among prenatal care registrants. The diagnosis of gestational diabetes was determined by 100-g, three-hour oral glucose tolerance test (GTT) results and/or repeated fasting serum glucose measures. RESULTS: In 1995, 69 women were referred to the gestational diabetes clinic with a 50-g result ≥200 mg/dL. Four women could not be classified, two had pregestational glucose intolerance and four charts were unavailable. Of the remaining 59 women, 11 (19%) had normal three-hour GTTs, and 48 (81%) were diagnosed with gestational diabetes (35 [59%], A ₁; 13 [22%], A ₂). There was one large-for-gestational-age (LGA) infant born in the nondiabetic group (9%), 13 LGA infants born in the A ₁ group (37%) and 6 LGA infants born to the A ₂ diabetics (46%). The relationship between maternal diagnosis and LGA outcome was statistically significant. CONCLUSION: A 50-g screening test result ≥200 mg/dL is not diagnostic of gestational diabetes. Nearly one of five such women had a normal three-hour oral GTT. Overdiagnosis of gestational diabetes may lead to unnecessary pregnancy surveillance and intervention.