Screening for fetal anomalies by ultrasound at 14 and 21 weeks

A prospective study of screening for fetal abnormalities and chromosomal defects was carried out by ultrasound examination at 13–l5 weeks of gestation and 20–22 weeks; the first scan was performed transvaginally and the second transabdominally. During a 4-year period (1991–95), 3490 unselected consecutive pregnancies with a total of 3514 fetuses were examined. There were 21 chromosomally abnormal fetuses, including ten with trisomy 21, and, in 19 (90.5%), fetal defects were detected at the first and/or second ultrasound examination. The most effective marker for chromosomal defects was increased nuchal translucency thickness (≥ 4 mm) at the 13–15-week scan, which was present in seven of the ten fetuses with trisomy 21 and in six of the 11 with other chromosomal abnormalities. Copyright © 1997 International Society of Ultrasound in Obstetrics and Gynecology