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

Objective: To compare the performance of the 50 g glucose challenge test (GCT) and the 100 g 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 14 797 women, of whom 14 268 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 > 130 mg/dl (20.2% versus 11.8%, p < 0.001) or GCT >140 mg/dl (13.8% versus 9.6%, p = 0.001). The positive prediction value (PPV) for a GCT >140 mg/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 >130 mg/dl [odds ratio (OR) = 2.2, 95% confidence interval (CI) 1.7-2.7] or >140 mg/dl (OR = 1.9, 95% CI 1.5-2.5) even after adjustment for maternal age, parity and fetal sex.
Conclusion: The 50 g GCT appears to be associated with a higher false positive rate and a lower positive predictive value in twin compared with singleton pregnancies.