Prenatal screening for Down syndrome with maternal serum human chorionic gonadotropin levels.

Human chorionic gonadotropin levels in midtrimester pregnancies may be predictive of Down syndrome. A commercially available enzyme immunoassay kit was used to measure the beta-subunit of human chorionic gonadotropin in maternal sera from 38 Down syndrome pregnancies and 114 gestational age matched controls. The human chorionic gonadotropin levels were also assayed in 236 normal sera and plasma samples to determine normative values and appropriate individual corrections. Serum and plasma human chorionic gonadotropin levels are closely correlated and are stable at room temperature, during refrigeration, and throughout freeze-thaw cycles. There is no correlation between the human chorionic gonadotropin level and maternal age, weight, or race. However, the human chorionic gonadotropin level decreases with each week of gestation from 15 to 19 weeks. Medians for each week of gestation were established to account for this variable. Up to 63% of the Down syndrome pregnancies were detected with a cutoff of 2.0 multiples of the normal median. A computational combination of human chorionic gonadotropin and maternal serum alpha-fetoprotein testing will detect additional Down syndrome pregnancies and decrease the false-positive rate. The measurement of human chorionic gonadotropin appears to be a valuable addition to maternal serum alpha-fetoprotein screening programs that can significantly increase the proportion of Down syndrome cases diagnosed.