Spaceborne and spaceborn: Physiological aspects of pregnancy and birth during interplanetary flight.

Crewed interplanetary return missions that are on the planning horizon will take years, more than enough time for initiation and completion of a pregnancy. Pregnancy is viewed as a sequence of processes - fertilization, blastocyst formation, implantation, gastrulation, placentation, organogenesis, gross morphogenesis, birth and neonatal development - each of which needs to be completed successfully, and each of which has a probability of success. The effects of the environment of interplanetary flight - microgravity and galactic cosmic rays (GCR) - on these probabilities are inferred from Earth and low Earth orbit experiments and observations and current models of morphogenesis. The principal hazards for intrauterine development are due to interactions with GCRs, where a variable flux of high energy particles would be interacting with a growing embryonic and fetal target volume, and produce linear tracks of ionization-associated damage. Short term damage would be predominantly mediated via reactive oxygen species, and long-term damage via DNA. Exposure to GCRs is expected to increase the probabilities of implantation failure and of premature labour. A live healthy birth would be possible, but its likelihood reduced. The long time scale of growth and development of the neonatal brain makes delayed manifestation of neurological or behavioural disorders likely.