How come a baby doesn't drown when they are in the womb but once there out they can?
Answer:
While they are in the womb they receive oxygen from the umbilical cord. Their blood travels from their heart through the cord to the placenta where oxygen and nutrients from the mom's blood are carried back to the body.
In addition before a baby is born their circulatory function does not work as an adults does. Blood does not fill the lungs. There is a duct between the vessel that would fill the lungs and the blood that goes to the rest of the body. So rather than deoxygenated blood going to the lungs, becoming oxygenated, returning to the other side of the heart and being pumped through the body returning deoxygenated to the heart and to the lungs. Oxygenated and deoxygenated blood are mixed and travel around freely.
After birth the baby breathes, this inflates the lungs which fill with blood; the duct closes. Circulation becomes as in the adult. It is very important that you not cut the cord before the lungs are full of blood, otherwise the baby will not have enough blood which can cause problems. Sometimes the duct doesn't close, then they try drugs and if that fails surgery.
So the reason a baby doesn't drown is the same reason someone on by-pass during surgery doesn't die. The blood is being oxygenated in a different way.
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