Question: How would a new born child grow within a zero gravity environment?

Steve Marsden answered on 7 Mar 2016:

While in space astronauts exert a lot less energy moving around as there’s no need to stand or walk. Because of this they need to exercise for four hours a day in an attempt to maintain muscle. So a child growing up in zero gravity would likely have very little muscle mass, possibly to the point of looking malnourished.

Every day when we walk, the spongy material between our spine’s vertebrae is compressed. Without that action the spine would be slightly longer. Potentially all bones would be slightly longer and more brittle.

We’re not certain about the long term exposures to zero gravity, but we know that after several months, the shape of the eyes changes. This is because fluid builds up behind them that would normally be helped to drain away be gravity. The reduces vision, and may cause blindness if the person remains in low gravity for years on end.

Assuming that we’re in space, then as well as the low gravity, there’s also radiation to deal with. In low Earth orbit this isn’t too bad. For an adult this slightly increases the chance of developing cancer in the future. For a baby/child however, the risk is far greater.

The radiation also brings on glaucoma. So if the eyes maintain their shape for long enough, the lens will ultimately cloud over.

There are probably many more effects that aren’t known yet, and this is a large part of the research that is currently being performed aboard the International Space Station.