First-trimester ultrasound

There has been an increase in the use of fetal ultrasound in the first trim ester. This article reviews the published literature with emphasis on fetal nuchal translucency (NT). When measured according to well-defined guidelin es, increased NT identifies about 80% of chromosomal anomalies for a false- positive rate of about 5%. Increased NT may indicate the presence of struct ural defects or genetic disorders, and it is relatively frequently seen in monochronic pregnancies prone to develop twin-twin transfusion syndrome.