Serum concentration of placental proteins in non-pregnant and pregnant subjects.

Chorionic gonadotrophin (hCG) and Schwangerschaftsprotein 1 (SP1) were measured in 35 menstrual cycles in 20 women. During the follicular phase, 3 samples were positive for hCG and two of these were also positive for SP1. All these positives occurred on the day of ovulation or immediately before. In the luteal phase 25 specimens showed both hCG and SP1 and two showed only SP1, the positive results occurring 3-15 days after ovulation. The placental proteins were also measured in a further eight women who became pregnant. The pattern in these was quite different. The first positives were detected 8 days after ovulation and by 12 days all the subjects were positive for both proteins. Thereafter both proteins increased sharply in concentration. A group of 139 subjects who, on biological grounds, could not have conceived, showed no positive results.