Chorionicity stands for the type of placentation and this is a very important issue because chorionicity is a significant factor, that will influence the perinatal course. The reality of expecting two babies with two placentas or two babies with one placenta is completely different, involving specific medical problems in the future. This information about the type of placentation is very important for the doctor in charge of a pregnant woman carrying multiples to know what kind of pregnancy he is dealing with. Therefore, it is of paramount importance to assess the correct gestational age, to know exactly how many weeks we ll have at the end when we want to terminate a pregnancy or when the delivery will spontaneously occur. Another important issue, not only concerning singletons but also multiples, is the screening of aneuploidies.
Aneuploidies are chromosomal abnormalities.
The most frequent aneuploidy is Down s syndrome or mongolism. When the karyotype of a fetus is abnormal, the parents should be informed in order to decide what to do with this pregnancy. One of the possibilities for assessing this risk is to measure nuchal translucency. Nuchal translucency is the fluid that accumulates behind the fetal neck and which thickness is measured by ultrasound between ten and fourteen weeks gestation. In the case of a monochorionic twin pregnancy, nuchal translucency can be also used for screening of an early onset hemodynamic overload.