A separate mechanism of gonadotropin recovery after pregnancy termination.

To further elucidate the mechanism of return of pituitary secretory function after gestation, eight women were studied for up to 55 days after pregnancy termination. As long as serum estradiol (E2) and progesterone (P) levels were elevated, serum FSH remained low. Four to 6 days after abortion, serum E2 and P decreased to levels seen in the early follicular phase, and thereafter the initial increase in FSH occurred while serum beta-LH remained undetectable. After the initiation of FSH secretion, the levels fluctuated within the normal follicular phase range, resulting in a steady increase of E2 to a mean preovulatory peak of 257 +/- 37 pg/ml at a mean time of 21 +/- 1.3 days after pregnancy termination. This E2 peak was followed by FSH and LH peaks and subsequent ovulation. In contrast to FSH, serum beta-LH levels increased only after PRL-concentrations diminished to 30 ng/ml or less. This initiation of beta-LH secretion followed the advent of FSH secretion in six of eight patients. Therefore, a temporally separate mechanism of FSH and LH secretion after pregnancy termination is theorized. The theory of FSH occurs soon after the E2 and P levels decline while PRL levels are still elevated. However, the secretion of beta-LH increases only after levels have risen from the postabortion decline.