Concentrations of immunoactive inhibin in serum during human pregnancy: evidence for an ovarian contribution.

Immunoactive inhibin (ir-inhibin) concentrations in maternal serum during normal human pregnancy have been established in two separate studies employing cross-sectional and longitudinal sampling regimes. Ir-inhibin concentrations rose from the mid-luteal phase (geometric mean + 95% confidence intervals 1.490 (1.086-2.028) U mL-1) to peak at week 11 of gestation (3.77 (3.26-4.35) U mL-1), declined to a plateau from 14 to 25 weeks with means ranging from 1.8 to 2.3 U mL-1, and subsequently rose slowly to a peak of 6.53 U mL-1 at 41 weeks. In the longitudinal study, similar results were obtained and no differences were found in maternal inhibin levels in women carrying male or female fetuses. Paired cord blood and maternal samples showed no significant difference in ir-inhibin concentrations irrespective of the sex of the fetus. However, in all such pregnancies amniotic fluid ir-inhibin levels were 2-3 fold greater than maternal or fetal levels raising the possibility that the amnion may secrete inhibin. In 12 women without functional ovaries in whom a singleton pregnancy was achieved by donation of oocytes and in vitro fertilization, the ir-inhibin levels showed a similar pattern in the first trimester of pregnancy but the concentrations achieved were markedly lower (peak 1.1 U mL-1 at 9 weeks). In five women from the group in whom samples were available late in gestation, three showed greater than normal levels and two had subnormal levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Contributions of in vitro fertilization to knowledge of the reproductive endocrinology of the menstrual cycle.

The administration of ovarian stimulants to endocrine-normal women in IVF programmes gives the clinical endocrinologist an opportunity to modify natural folliculogenesis. Use of antioestrogens and/or gonadotrophins at the correct time has demonstrated that follicular atresia can be prevented and that multiple pregnancy-potent haploid ova can be obtained. Scrutiny of spontaneous menstrual cycles in patients who show unsatisfactory IVF responses has identified two new syndromes, premature follicle selection and occult ovarian failure, in these patients. The incidence of these disorders in fertile women is still unclear. Early results suggest that endocrine manipulations may overcome premature follicle selection and induce codominant folliculogenesis. Inhibin is a recently characterized ovarian protein which is increased in peripheral blood during IVF treatment. Results from IVF cycles suggest that plasma inhibin may be a new index of follicular function. Other potential indices of ovarian function, such as the luteal protein relaxin, may also develop from the application of basic research to IVF and advance knowledge of the human ovarian and menstrual cycles.