Table 2 summarizes the results of spaceflight on female reproduction. Despite speculation that headward fluid shifts, cardiovascular deconditioning, bone demineralization, and decreased red cells associated with hypogravity may affect the ability of rat dams to sustain their pregnancy, the results of spaceflight studies indicate that pregnant rat dams are able to successfully direct physiological resources to support fetal development in the space environment. In females, appropriate ratios of estrogen and progesterone are required for the establishment, maintenance, and termination of pregnancy. In view of the changes in male reproductive hormones following spaceflight, there is concern that spaceflight also may affect female reproductive hormones.
However, Burden et al. reported no change in estrogen and progesterone levels in pregnant spaceflight rats. Spaceflight rat dams did experience an increased number of contractions during parturition due to reduced connexin 43, the major gap junction protein in the myometrium that plays a role in the synchronization and coordination of contractions. Although contractions in spaceflight rat dams were increased, there were no effects on fetal wastage, birth weight, litter size, or maternal care of the neonates. Although progress has been made in the area of late pregnancy and neonate development, more studies are needed on fertility, conception, and early pregnancy in space. Ground-based models are well suited to address these existing gaps in our current knowledge.