Hello Thank you for your query. Complete placenta previa is when the placenta occupies the lower pole of the uterus. Normally it is situated in the upper portion. Thus, it leads to bleeding frequently. It is a serious condition. Constipation has no association with the bleeding, as bleeding is due to the placenta previa, however, straining at stools can trigger a bout of bleeding. Normally, 90 % of low lying placentas migrate upwards by the third trimester. However, if it is a COMPLETE previa ( placenta completely in the lower part ), chances of migration are less. You are at risk for recurrent bleeding, preterm labour, malpresentations, growth restriction of baby and many other complications. Please follow bedrest, avoid sexual activity. take care.