Fetal Aneuploidy: A Comparison of Dichorionic Twins and Monochorionic Twins

To assess the clinical characteristics of fetal aneuploidy between dichorionic twins (DCT) and monochorionic twins (MCT) undergoing invasive prenatal diagnosis.

Twin fetuses undergoing invasive prenatal diagnosis were enrolled in this study. All twin fetuses were classified into 2 groups according to chorionicity. The rates of fetal aneuploidy in different groups were compared.

This study included 1,714 fetuses (857 sets of twin pairs); among them, 1,190 were DCT and 524 were MCT. Overall, the rate of aneuploidy was 4.7% (56/1,190) in DCT and 3.4% (18/524) in MCT. Sixty-four (86.5%, 64/74) fetal aneuploidies occurred in only one fetus of the twin pairs. In DCT, the most common aneuploidy was trisomy 21 (53.6%, 30/56), followed by trisomy 18 (21.4%, 12/56) and trisomy 13 (8.9%, 5/56), while in MCT, the most common aneuploidy was Turner syndrome (33.3%, 6/18), followed by trisomy 21 (27.7%, 5/18) and 47,XYY (11.0%, 2/18).

Aneuploidy mostly occurred in only one fetus in the twin pairs. The most common aneuploidy was trisomy 21 in DCT and Turner syndrome in MCT. Dual amniocentesis should be performed when discordant monozygotic twins are suspected.