Why is the bleeding painless from placenta previa?

Placenta prevIa: The stretching of lower uterine segment causes the disruption in blood supply to the plaventa. The blood usually comes out of the internal os. So this bleeding is painless. Rarely is there is collection of blood behind placenta than it can be painful.

No contractions.: Because the bleeding does not involve the contractile part of the uterus, only the placenta over the cervix. The placenta is devoid of innervation, therefore the mother does not experience pain in bleeding previa unless preterm labor is also present.

Leaky placental vsls: Previa: Placenta overlies the cervix/birth canal. Gr 1 means placenta is close, Gr 4 means it's directly overlying/blocking the baby's exit -- high chance of preterm labor & bleeding; you'd need a C/S at 36-37wks. More common in woman w/ hx of C/S & smoking. Not much you can do but wait. If dx'ed early, the uterus still grows/stretches and a placenta can migrate away even in 3rd tri. Follow w/ US.