The radioimmunoassay of a pregnancy specific-beta 1-glycoprotein in plasma as a pregnancy test for subfertile women.

We used a pregnancy specific-beta 1-glycoprotein (SP1) radioimmunoassay to monitor 72 menstrual cycles of 38 apparently subfertile women who were trying to become pregnant. Blood samples were taken up to day 42 from the start of the previous menstrual cycle. Using serum SP1 levels greater than 6 micrograms/1 as indicative of pregnancy, we obtained 16 positive results of which 11 were later confirmed by a human chorionic gonadotrophin haemagglutination pregnancy test. Three of the five women whose pregnancies were not confirmed had a subsequent history of spontaneous abortion.