Concentrations of pregnancy-specific beta 1-glycoprotein in maternal blood in normal pregnancy and in intrauterine growth retardation.

A radioimmunoassay has been developed for pregnancy-specific beta 1-glycoprotein (S.P.1), a product of the human placenta. Circulating concentrations of S.P.1 were measured in 153 women in the third trimester of normal pregnancy and in 27 women who delivered children with birth-weight below the 10th centile of the normal range--i.e., with intrauterine growth regardation (I.U.G.R.). Concentrations of S.P.1 showed a skewed distribution and rose progressively to reach a plateau in the last four weeks of pregnancy. In over 70% of women with I.U.G.R. of the fetus, concentrations of S.P.1 were low. Measurement of serum-S.P.1 may provide a new index of fetal wellbeing.