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

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.

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.

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.

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.