Something that blows my mind about pregnancy is that your body is housing an organism that is genetically half someone else.
Half of your baby's DNA comes from the father. Your immune system knows this. It recognizes the foreign DNA. And instead of attacking it, your body actively builds tolerance around it for nine months.
A 2025 study identified a specific immune cell responsible for a big part of how this works. CCR8 decidual regulatory T cells sit at the uterine lining and actively suppress the local immune response so the pregnancy is protected. When researchers removed these cells in mice, the immune environment turned hostile and pregnancy loss went up. When they put the cells back, the pregnancies were rescued.
There are multiple systems working together to make this happen, but this is one of the clearest pictures we have of how the body pulls it off.
Your body is running a coordinated immune operation the entire pregnancy and you have no idea that any of this is happening.