Antenatal screening

Abstract

Screening aims to identify high risk individuals for prenatal diagnosis. Maternal serum α-fetoprotein (AFP) screening at 16–18 weeks gestation detects about 90% of anencephalics and 75% of spina bifidas for a 2% false-positive rate. Routine ultrasound anomaly scanning at 18–20 weeks yields even greater neural tube defect (NTD) detection, fewer false positives and detects other structural abnormalities. Of the seven established second trimester maternal serum markers of Down's syndrome, a four marker combination detects over 72% for a 5% false-positive rate. First trimester maternal serum and ultrasound screening for aneuploidy is now feasible. Pilot studies of multiple mutation screening for cystic fibrosis (CF) show high acceptance rates. DNA screening for fragile X syndrome is predicted to detect almost every affected pregnancy for a 0.4% false-positive rate.