Screening and diagnosis of chromosomal abnormalities in twin pregnancy.

Twin pregnancies are at an increased risk of adverse pregnancy and perinatal outcome as compared to singleton gestations, mainly as the consequence of the higher rate of preterm birth, chromosomal as well as structural anomalies, placental abnormalities, and complications unique to monochorionic placentation. Screening for chromosomal anomalies poses diagnostic and management challenges when applied to twin pregnancies. The recent implementation of cell-free fetal DNA (cffDNA) in clinical practice raises the questions whether a more accurate test should be offered to twin pregnancies in view of the higher false positive rate of traditional screening and the higher risk of fetal loss following amniocentesis or chorionic villus sampling (CVS) in multiple gestations. Finally, twin pregnancies require a tailored approach for aneuploidy screening, such as nuchal translucency (NT) or crown rump length discordance, discordant fetal anomalies, or monoamniotic gestations. The present review aims to provide an up-to-date critical appraisal of screening and prenatal diagnosis of chromosomal abnormalities in twin pregnancies.