A circumvallate placenta is a placenta that does not form properly. This placental abnormality occurs in less than two percent of pregnancies and it is not the fault of anything the mother does or does not do. It occurs because of variations in placental development that are beyond the control of the body that the fetus is gestating in. When a woman is diagnosed with a circumvallate placenta, it is important to receive adequate prenatal care because it increases the risks associated with the pregnancy.

In pregnancies with a circumvallate placenta, the chorionic plate on the fetus' side of the placenta is slightly too small. Over time, a ring of raised tissue develops and the ends of the placenta start to turn inward. This restricts the supply of nutrients to the growing fetus and can also increase the risk of a placental separation. There are some serious risks associated with this complication of pregnancy.

In the worst case scenario, circumvallate placenta can result in pregnancy loss. If the placenta separates and a woman is not given immediate medical treatment, the baby can die. In women who have not received adequate prenatal care where the condition goes undiagnosed, fetal deaths can also be caused by the nutrient restriction associated with this condition. More commonly, women with this condition will need to deliver by cesarean section and their babies may have a low birth weight.

This condition can be diagnosed with a routine prenatal ultrasound. Physical abnormalities can be observed on the ultrasound examination in varying levels of detail, depending on the technology used for the exam. The doctor may note that the fetus is not growing as quickly as normal and this can also provide clues to the fact that there is an abnormality. For women with a circumvallate placenta, it is important to eat a healthy diet to ensure that as many nutrients as possible reach the baby, and to be alert to spotting, breakthrough bleeding, and uterine pains that might indicate complications with the placenta.

Women can and do deliver healthy babies with a circumvallate placenta. The chances of a healthy birth increase with each week that the woman can successfully carry the pregnancy. An obstetrician may have specific advice for a patient including bed rest if it becomes necessary to help her carry the pregnancy to term. Women with this placental abnormality should also make sure that they discuss their birth plans carefully with their doctors.