Effect of Advancing Pregnancy on the Glucose Tolerance Test and on the 50-g Oral Glucose Load Screening Test for Gestational Diabetes

Abstract

To determine the validity of the 50-g, one-hour glucose screening test for gestational diabetes in relation to the duration of pregnancy, 101 patients from a high-risk population had the screening test in the first trimester and glucose tolerance tests (GTT) in the second and third trimesters. The sensitivity (88%) and specificity (82%) of the screening test were similar to values reported when the test is performed later in pregnancy. However, immediate follow-up GTTs in the second trimester revealed only 25% instead of 88% of the gestational diabetic patients uncovered by the positive screening tests. Guidelines for screening for gestational diabetes should include follow-up with a third-trimester GTT on all patients who have positive screening tests even in the presence of normal follow-up second trimester GTTs.(Obstet Gynecol 68:362, 1986)