Anovulation after Pregnancy Termination: Ovarian Versus Hypothalamic-Pituitary Factors

Abstract

To differentiate hypothalamic-pituitary from ovarian factors responsible for postgestational suppression of folliculogenesis, 28 rhesus monkeys were studied after either surgically induced abortion 21 days after fertilization or spontaneous delivery at term (167 days). Ovarian refractoriness was evaluated by the administration of low doses of human menopausal gonadotropin to stimulate follicular maturation. Alternatively, estradiol benzoate was injected to test for induction of gonadotropin surges. Resumption of spontaneous ovulations was delayed until 38.4 ± 5.7 days (mean ± SE) after induced abortion, whereas sham abortion did not deter cyclic ovarian function in nonpregnant monkeys. That folliculogenesis had been stimulated by human menopausal gonadotropin both post abortion and post partum was confirmed by the presence of multiple preovulatory follicles on both ovaries (n = 3-7⁄ovary), as assessed at laparotomy, and by concurrent elevations of serum 17⁄?-estradiol (P < 0.01). hCG therapy caused final maturation and rupture of all or most of these preovulatory follicles within 24 h, as indicated by the development of multiple stigma and subsequent increases in serum progesterone levels. The interval from abortion to induced ovulation was 12.5 ±1.3 days and from delivery until induced ovulation was 12.2 ± 1.8 days. Resumption of estradiol benzoate-stimulated gonadotropin surges was not apparent until 21 days post abortion or 35 days after fullterm delivery. These findings demonstrate that pregnancy does not impart any apparent refractoriness to gonadotropic stimulation on the ovaries directly but, rather, establishes a gestational (duration-dependent) suppression of hypothalamic-pituitary function. Although tonic gonadotropin secretion may also be inadequate to support folliculogenesis post partum, responsivity to the positive feedback actions of estrogen on FSH and LH surges is impaired transiently for about 5 weeks.