Ultrasound of the fetus during the first trimester

Abstract

Ultrasound (US) examination at 11-14 weeks of gestation aims to confirm the gestational age, determinate chorionicity for multiple pregnancies, measure the nuchal translucency (NT) thickness to assess the risk of aneuploidy, and to visualize the basic anatomical structures of the fetus (Guidelines of the Fetal Medicine Foundation, London; http://www.fetalmedicine.com). Despite the lack of clear checklist for the ultrasound examination of the fetal anatomy, during the first trimester, several studies have described in great details the evolving anatomy of the fetus during this period and thus number of nonchromosomal abnormalities allowing an early termination of pregnancy. Nevertheless, a significant number of major anomalies have late onset and are not detectable in the first trimester ultrasound and the second trimester scan remains necessary.