How does vasa previa occur?
The theory about this that makes most sense is called Trophotropism. The easiest way to explain this is to make a comparison to a plant. A plant will lean towards the sun to get the light it needs to survive. Since the lower segment of the uterus is not as nourishing as the upper segment, the placenta will grow to reach more nourishing tissue. The placental mass will erode away from the cervix, but the vessels can’t. This also explains the velamentous insertion of the cord. That the mass may erode and the new growth may occur away from the location where the cord inserts.
