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What would the effects of pregnancy in space environment be on a human fetus? I understand that astronauts on long-duration missions in microgravity environment experience bone density loss. Would that be a concern for human embryonic development, and if so, what precautions could be taken to avert bone growth / bone density issues?

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We don't know. There was some research done on embryonic development of mice and rats in microgravity, both impregnated females sent to orbit and later recovered (mostly onboard Space Shuttle, but Russians also sent in orbit similar experiments), and even more frequently by using 3D clinostat to simulate microgravity via continuous three-dimensional rotation. Reduced number of successful full-term pregnancies was observed for females exposed to microgravity during early pregnancy, while fewer abnormal pregnancies for those exposed later. Findings suggest that embryonic stem cells have problems developing normally under microgravity conditions during early pregnancy and result in abnormal fetal development and terminated pregnancy.

So even if impregnation alone is not a problem, and it might be, due to increased radiation adversely affecting male fertility and sperm count, I dread to think what a full-term human pregnancy would result in, without intervention of biotechnology and biomedical engineering that can hopefully one day develop solutions to abnormal cell division and protein growth in microgravity. Increased frequency of cell mutations due to increased radiation is also not excluded, considering full-term human pregnancy lasts on average about 38 weeks, and for mice, gestation period is between 19 and 21 weeks, and rats a week or two more. With those sent in orbit already impregnated (or fertilized in-vitro) 9-20 days before launch, this means we only have experimental data on exposure duration of roughly half full-term human pregnancy duration.

So regarding bone density, it's really hard to judge without any observational data. All we have are observations done on adult humans and smaller mammals, mostly rodents. Common sense suggests that human embryos, since they develop in uterus and placenta filled with water providing some unidirectional pressure on the developing embryo even in microgravity, shouldn't have problems developing sufficient bone density, assuming normal (for gravity) protein growth can be achieved during early pregnancy. Of course, once we have that capability, we have also solved bone density problems of adult astronauts on long duration microgravity missions.

Before that though, I'd personally rather no one even tries. And it might not be down to my personal preference either, there are all kinds of should we ethical questions to consider for planned human pregnancy experiments in microgravity, before we answer the ultimate one: Do we really have to?

Further reading and references:

Documents in Russian (Abstracts in English):

Related posts on Space Exploration:

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