A.S.
I read a lot of medical journals when I was on bed rest. Here's what I remember:
An enlarged placenta can be caused by a number of things or it can just be the way the placenta is. Women who smoke sometimes have enlarged placentas. It can also be caused by diabetes or anemia or infection. Sometimes if you don't get enough protein it can cause placental problems. It usually results in the mother being more closely monitored than a 'normal' pregnancy but more often than not everything turns out fine.