Oyama et al. reported that pregnant rat dams centrifuged at 2.16 or 3.14 g had reduced numbers of survivors within their litters compared with 1-g controls. Furthermore, neonatal mortality in this study increased with increasing g load. Survival and development of neonates in hypergravity is partly dependent upon normal maternal behavior and mother-offspring interactions. Decreased plasma prolactin in rat dams centrifuged at 2.16 or 3.14 g has been suggested as a mechanism responsible for decreased neonatal survival because prolactin plays a key role in the expression of maternal behavior in rats.
Because maternal care may be influenced by previous experience, Ron-ca et al. compared primigravid and bigravid rats exposed to 1.5 g centrifugation at Gestation Days 11-22. Pup survival was 82% for primigravid dams, 94% for bigravid dams, and 99% for 1-g controls, suggesting that previous maternal experience is protective against neonatal loss. These study results indicate that altered gravity affects reproductive physiology during pregnancy and lactation and affects maternal behavior and mother-offspring interactions. Further ground-based studies are needed to provide a more detailed understanding of the issues of pregnancy, birth, and rearing of offspring in space.