Placenta Previa

Start with one picture. The placenta has implanted over the internal cervical os, the one part of the uterus that must stretch, thin and open before birth. As that lower segment changes, the attachment above the os is pulled apart and maternal vessels tear. Blood has a direct path out through the cervix, so bleeding is often visible, sudden and painless. The fetus has not usually lost its oxygen supply at that moment, and the mother is the one bleeding. Everything in the care of this patient follows from that picture: protect the os, quantify the blood, watch the mother first and plan a birth that does not pass through the placenta. Placenta previa occurs in about 4 to 5 of every 1000 pregnancies, so most nurses will meet it, and its incidence rises with the number of uterine scars in a population. Risk factors explain why the placenta came to rest in the lower segment, and they also predict how dangerous delivery will be. The primary risk factor for placenta previa is a history of prior caesarean birth. A...