A Baby Born in Space

By: Patty Currier
Payload Scientist NASA Kennedy Space Center, Cape Canaveral, FL. 
August 26, 1999


I was recently contacted by Brandt Secosh who had received a question from Nur Agustinus, a student in Indonesia, regarding the birth of a baby in space (microgravity). I thought this was an interesting question that should be shared with all of the Space Team Online followers!
First, the question:

If a baby were born in space (microgravity) and grew up there, would it influence the structure of the bone or body? Would microgravity cause the muscles to be smaller than a child growing up normally on Earth?

I work with a lot of students here at Kennedy Space Center, but before I started doing this, I worked in a bone lab. So I think I can help you with your question.
This is for a lady who is going to have a baby as soon as she gets in space. Things will be more complicated if the fetus develops in space and is then born, so I'm not going to try to answer that one yet.

If a pregnant woman flies in space and gives birth almost right away, the baby will be born pretty normal because it will develop in the womb very normally at Earth's gravity. What happens then is very interesting.

The bone cells are programmed to grow--they don't stop until you are a teenager or so. But it is gravity as a stress that makes the cells in the bones have the right alignment, or stack up properly and pull the bone so that it forms straight. Without gravity, the baby's bones won't get long and thin like adult bone. They will be very easy to break, and they won't grow as fast. This is true for arms and legs. 

The bones at the top of the baby's head will actually grow thicker and stronger than on Earth. This is because your heart does not have to work so hard to move blood and other fluid from your feet to your upper body because there is no gravity. What happens is that the heart still pulls on the fluid in the legs, which now comes out much more easily. This causes the upper body to have more fluid and more pressure, which causes stress. Stress is always what makes bone grow and change. So, more pressure, more growth in the skull.
The bones in the hands will probably be normal because the baby/child/adult will use his hands just like on Earth. The feet will probably not grow much because they don't get the stress from having the weight of your whole body on them--no stress, not much growth. Ribs are interesting. Ribs protect your lungs and give support to your body so they don't collapse. They would probably be okay, but develop thinner than on Earth, so they wouldn't be nearly as strong. The spine is really going to be affected. The gravity won't push / pull down on you, so the vertebrae don't feel the stress, so they won't grow. But they will get stress from the spinal cord as it grows and pushes out. So you would probably end up with thinner, very easily crushed vertebrae.

Muscles work the same way. They need stress to grow and develop. Gravity is a stress force that pulls in one direction causing the muscle to develop in the right shape. So, if it is a muscle that won't be used much (say, the muscles that move your feet), they won't grow nearly as strong. Some muscles will be almost the same, such as your hand muscles. They aren't much affected by gravity--they are more affected by how the other muscles in your hands contract and release. They are stressed independently of gravity. Other muscles, like your heart, will be different. Your heart won't have to work as hard because there is no gravity to make blood circulation difficult. This takes a while to happen though. With a baby just born, probably the heart will never develop nearly as strong as a baby on Earth will. 

Muscles and bones work together. The muscles are attached to bone, and they are very tightly connected. If you exercise a muscle, it pulls on the bone and causes a pulling stress. This helps the bone grow stronger in that area. This is why kids are told to play around outside when they are young--their bones grow very fast and if the child does a lot of exercise, the muscles get strong, making the bone very strong. 

So, a baby born in space is going to have pretty strange and weak bones in most parts of their body. This shouldn't affect them too much if they spend their whole life in space, but they will be in a lot of trouble if they come back to Earth. Their leg and feet bones will be too weak to hold them, the spine will probably crush under its own weight. The heart muscle will not be strong enough to pump blood around the whole body because of gravity pulling the blood down, and leg muscles will be too weak for you to stand. Basically, your bones and muscles will be much too heavy to support, and you will fall down in a big heap and die - (unless the mother is very insistent and special equipment is made so the baby can exercise muscles and bones to make them similar to the ones on Earth -but you still have heart and other things...).

But if you are a baby born in space and someone drops you on your head when you return to Earth, your skull will be nice and thick.

Isn't bone a really neat thing?