As the frequency of multiple pregnancies is increasing, every obstetrician has to know that the correct, accurate, and timely determination of gestational age, chorionicity, and amnionicity has significant importance in the management of a multiple pregnancy. Surveillance, complications, outcome, morbidity, and mortality are totally different in a monochorionic and a dichorionic pregnancy. In this chapter, we will present the sonographic figures that are visualized in the first trimester in a multiple pregnancy and help us define the gestational age, chorionicity, and amnionicity. We will classify them into two periods: the early first trimester, including the 10 first weeks of gestation and the late first trimester including the period between the 10th and 14th week of gestation. Finally, we will review some interesting, although infrequent, cases from the literature, showing that pitfalls in the determination of both chorionicity and amnionicity exist and highlighting the importance of being aware of their subsistence.
Part of the book: Multiple Pregnancy