Happy Mother’s Day, from all of your children!

It turns out our babies are always with us, in more ways than you might have imagined. We used to think that fetal and maternal circulation didn’t mix. Then it was thought that this could occur following a trauma or at birth, such as in Rh sensitization (when an Rh negative mom is carrying an Rh positive baby and their blood cells mix in the mom, causing her to develop Rh antibodies). However, fetal cells can be found in maternal circulation decades after birth, even if a pregnancy wasn’t carried beyond the first trimester. This Radiolab podcast discusses how the result of this mixing might be one of the best Mother’s Day gifts ever.