The human menstrual cycle: plasma concentrations of prolactin, LH, FSH, oestradiol and progesterone in conceiving and non-conceiving women.

Hormonal profiles were obtained throughout 26 conception cycles and 27 non-conception control cycles. The pregnancies followed treatment (clomiphene or bromocriptine) in 12 women but were spontaneous in the remaining 14. No sustained significant difference between the various types of conception cycle was found for LH, FSH, oestradiol or progesterone concentrations. Prolactin concentrations varied widely, suggesting that mean cycle prolactin concentrations ranging from 45 to 760 mi.u./l are compatible with conception. Although there were no significant differences in progesterone secretion within the conception cycles, there were highly significant differences between the conception cycles and the non-pregnant control cycles. Mean progesterone concentrations in the conception group were higher (P less than 0.005) than those in the control women over Days 3-8 following the LH peak. This difference could only be partly accounted for by heterogeneity within the control group (15-20% of the control cycles had low progesterone concentrations and were probably subfertile. It is suggested that the higher conception cycle progesterone concentrations during the early part of the luteal phase may constitute a preimplantation component of the maternal recognition of pregnancy in women.