Concomitant secretion of Schwangerschaftsprotein 1 and human chorionic gonadotrophin following conception

Daily measurements of serum oestradiol, progesterone, Schwangerschaftsprotein 1 (SP1) and hCG were made in 13 menstrual cycles during which conception occurred. The assays were continued until 21 d after ovulation. SP1 was detected in maternal blood 8-14 d after ovulation and hCG 9-13 d after ovulation. We conclude that these two proteins are secreted simultaneously but independently by the syncytiotrophoblast.