Screening of Maternal Serum for Fetal Down's Syndrome in the First Trimester

Approximately 2.5 million pregnant women now undergo screening of serum for Down's syndrome each year in the United States. 1 Nearly all this testing is carried out in the second trimester. The first serum marker found to be associated with Down's syndrome was alpha-fetoprotein, the measurement of which was already being used as a screening test for open neural-tube defects. 2 – 4 In 1987 and 1988, other serum markers were found to improve the sensitivity of screening, notably human chorionic gonadotropin (hCG) 5 and unconjugated estriol. 6 The discovery of these markers was based on case–control studies using stored second-trimester serum samples from pregnant . . .