The number of female astronauts is growing, and the presence of women on long-duration spaceflights and at the International Space Station is also expected, yet relatively little is known about the effect of spaceflight on female reproduction. Environmental conditions can exert a number of adverse effects on the ovaries. To our knowledge, no researchers have examined the effect of the space environment on the ovaries of nonpregnant females. However, examination of the ovaries of postpartum rats flown in space during Days 9-20 of gestation showed no effect on ovarian weight or number of preovulatory or atretic follicles.
According to Ying et al., the mechanism mediating postpartum ovulation is the same as that in nonpregnant rats, suggesting that spaceflight does not affect the ovaries. Reproductive changes do not always occur at the ovaries but may occur at the hypothalamus or pituitary. The HPG axis regulates the ovulatory cycle, which is highly susceptible to environmental factors. For example, stress can lead to ovulation failure. Thus, the amount of stress experienced during spaceflight might be correlated with negative effects on the ovulatory cycle, but this possibility has not been explored. No data on women have been collected because female astronauts suppress their menstrual cycles during spaceflight. Animal studies of altered gravity examining ovulatory cycles are also scarce. In postpartum spaceflight rats, ovulation was suggested to be suppressed based on findings of reduced pituitary LH; however, measurement of plasma LH indicated no change.