Age‐adjusted ultrasound risk assessment for fetal Down's syndrome during the second trimester: description of the method and analysis of 142 cases

Abstract

AAURA permits improved individual counselling regarding the risk of fetal Down's syndrome following a second-trimester sonogram. For low-risk women under age 35 years, ultrasound assessment can identify over half of the affected fetuses with Down's syndrome with an acceptable false-positive rate (4%). For women aged 35-39 years, a normal ultrasound can substantially reduce the risk of unnecessary amniocentesis (12.5% from 100%) but will also miss approximately one-third of affected fetuses. Biochemical screening of maternal serum is also suggested for this group. Based on their high a priori risk, women aged 40 years or more should consider genetic amniocentesis regardless of a normal ultrasound.