[Trisomy 18 in a bichorial-biamniotic twin pregnancy].

Screening for chromosomal abnormality such as trisomy 18 in a bichorial-biamniotic twin pregnancy is based on ultrasound and a non-invasive prenatal test (NIPT) from 12 weeks of gestation. An invasive examination such as amniocentesis is necessary for a diagnostic confirmation. The management of these complicated cases consists in performing a selective feticide in the first or third trimester of pregnancy. Trisomy 18 most often results from a chromosomal nondisjunction of maternal origin. Indeed, advanced maternal age is a major cause of chromosomal abnormality and a promoting factor of twin pregnancies. This is a severe condition with a very high stillbirth rate, even though there are certain cases where babies have managed to survive for several years.