Varicose veins of the rectum, afflicting 20 to 50 percent of pregnant women. Caused by increased blood volume and pressure from the uterus on the veins in the pelvis, the swollen veins in the rectum look like a pile of grapes and cause itching, pain, and bleeding. They can also appear postpartum as a result of pushing during labor. Constipation can cause hemorrhoids or compound them.