Dimeric inhibin A and alpha-subunit immunoreactive material in maternal serum during spontaneous and in vitro fertilization pregnancies.

To increase our understanding of the nature and source of immunoreactive inhibin-related material during pregnancy, we studied inhibin secretion in women pregnant after spontaneous conception and after in vitro fertilization (IVF). Two solid phase enzyme-amplified immunoassays (EASIAs) were used to measure the inhibin A dimer and inhibin alpha-subunit immunoreactivities (alpha-inhibin). In spontaneous pregnancies, levels of both inhibin A and alpha-inhibin were low during the first two trimesters of pregnancy, but a significant increase was observed toward the end of gestation. Both assays confirmed that inhibin concentrations in IVF pregnancies exceeded those in spontaneous pregnancies during the entire first trimester. Moreover, the two assays displayed discordant profiles. The alpha alpha-EASIA, which detects all alpha-inhibin immunoactivity, displayed a major peak during the follicular phase and a second broader peak during the luteal phase and corpus luteum rescue. A progressive decline was observed during the subsequent weeks. EASIA measurements for inhibin A revealed distinct peaks during the follicular phase, the luteal phase, and the hCG peak. A marked fall, however, was seen at the time of corpus luteum rescue. In summary, these data indicate that the nature of the immunoreactive material changes considerably during the different phases of pregnancy. The available evidence further points to an ovarian source of dimeric inhibin in early pregnancy and a placental source toward the end of pregnancy.