I’m starting a new series about babies called Woven Together because the development of a little person is fascinating. For the most part, this series will deviate from the main content of the blog – how things go wrong – to tell how things go right. I hope you enjoy!

Babies in the womb have to make some adjustments to account for the fact that they’re in the womb: there’s no air to breathe and no food to eat. Today, we’re going to learn how their adjusted circulatory system works.

First off, mother and baby don’t share blood. They have two completely separate circulatory systems.1 Baby’s heart starts beating about 22 days after conception so that he can pump his blood to deliver nutrients to all the parts of his rapidly-growing body. The heart is baby’s first organ to

  1. That’s how mother and baby can have two separate blood types with relatively few problems. []