Second trimester maternal serum pregnancy specific beta-1 glycoprotein (SP-1) levels in normal and Down syndrome pregnancies.

Maternal serum pregnancy specific beta-1 glycoprotein (SP-1) levels in the second trimester may be predictive of Down syndrome (DS). An enzyme immunoassay was used to measure SP-1 sera from 46 DS pregnancies and 117 normal control women matched for maternal age, gestational age, and length of storage. In the normal control samples, there were slight correlations between the SP-1 concentration and maternal age. The maternal serum SP-1 levels increased with each week of gestation from 15 to 20 weeks. All but one of the DS sera had SP-1 levels greater than the normal median. Using a cutoff of 2.8 multiples of the median (MoM), 15.2% of the DS pregnancies were detected with a false-positive rate of 4.3%. A combinational logistic regression analysis of maternal age and pregnancy related serum proteins will detect additional DS pregnancies and decrease the false-positive rate. The combination of maternal age and SP-1 detected 33 (71.7%) of Down syndrome pregnancies. The addition of maternal serum alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG) levels allowed for the detection of 36 (78.3%) of the DS pregnancies with a decrease in the false-positive rate to 3.4%. The measurement of other serum constituents in conjunction with AFP appears to be a valuable addition to current screening programs, as this can increase the proportion of DS cases detected prenatally.