Placenta previa is a condition where the placenta grows over the cervix or is too close to the cervix. This can lead to catastrophic bleeding for both mother and fetus and requires a c-section for safe delivery.
Placenta previa is often suspected early on in pregnancy when an ultrasound suggests the placenta is very close to the cervix, however, weeks later when the ultrasound is repeated the placenta has moved. This is obviously good news, but how does that physically happen? After all, the placenta has invaded into the uterine wall so it can’t exactly pick up its things and walk up to another spot in the uterus like you would on the beach when you realize your planted your umbrella and towel below the high water mark and have now noticed the tide is coming it!
The answer is the placenta doesn’t move, the lower uterine segment beneath it grows. I made a short video to explain: