The performance of the screening test for gestational diabetes in twin versus singleton pregnancies

Objective: To compare the performance of the 50g glucose challenge test (GCT) and the 100g oral glucose tolerance test (OGTT) in twin versus singleton pregnancies. Methods: A retrospective study of all women who underwent a GCT (24-28 weeks) and delivered in a single tertiary medical center (2001-2012). The performance of the GCT and the OGTT tests were compared between twin and singleton pregnancies. Results: The results of the GCT were available for 14797 women, of whom 14268 were singleton and 529 were twin pregnancies. Women in the twins group were characterized by a higher mean GCT result (104.7±28 versus 98.5±25, p<0.001), a higher rate of GCT>130mg/dl (20.2% versus 11.8%, p<0.001) or GCT >140mg/dl (13.8% versus 9.6%, p=0.001). The positive prediction value (PPV) for a GCT >140mg/dl was significantly lower in the twins group for the prediction of either ≥1 abnormal values (21.1% versus 33.8%, p=0.03) or ≥2 abnormal values (12.7% versus 23.0%, p=0.04) in the OGTT. Twin pregnancy was independently associated with an increased risk for a GCT result >130mg/dl [odds ratio (OR)=2.2, 95% confidence interval (CI) 1.7-2.7] or >140mg/dl (OR=1.9, 95% CI 1.5-2.5) even after adjustment for maternal age, parity and fetal sex. Conclusion: The 50g GCT appears to be associated with a higher false positive rate and a lower positive predictive value in twin compared with singleton pregnancies.