First-trimester free beta (hCG) screening for Down syndrome.

Maternal serum free beta (hCG) levels are elevated (median 2.20 MOM) in the first trimester of pregnancy in 38 Down syndrome cases as compared with appropriate controls. This observation may form the basis for its use as a marker in screening for Down syndrome in the first trimester. Altered levels of the free beta analyte are observed in pregnancy conditions or complications other than Down syndrome.