Maternal serum free beta-hCG at 10 to 14 weeks of gestation in trisomic twin pregnancies.

Maternal serum free beta-hCG was measured at 10 to 14 weeks of gestation in 136 normal twin pregnancies and in 12 twin pregnancies where one or both fetuses had trisomy 21. The values were compared with a normal range from 4181 singleton pregnancies. In the normal twins the median free beta-hCG (65 ng/mL) was about twice as high as in singletons (34 ng/mL z = -12.1, P < 0.0001). In the trisomy 21 group the median free beta-hCG (95 ng/mL) was significantly higher than in normal twins (z = 2.1, P < 0.05). However, only one of the trisomic pregnancies had a level above the 95th centile. In twin pregnancies maternal serum free beta-hCG at 10 to 14 weeks of gestation is unlikely to be useful in the prediction of fetal trisomy 21.