Blighted ovum: What causes it?

Blighted ovum is an older term for a certain type of pregnancy that leads to an early miscarriage. It's now known as an anembryonic (an-em-bree-on-ik) pregnancy.

With a healthy pregnancy, an egg fertilized by sperm develops into the earliest form of an unborn baby, called an embryo. But with an anembryonic pregnancy, an embryo never forms, or it stops forming and is reabsorbed by the body. The reason this happens is often unknown. But it may be due to problems with chromosomes — the structures that contain genes — in the fertilized egg.

Most often, an anembryonic pregnancy occurs early — sometimes before you even know you're pregnant. But you may be aware of your early pregnancy because of a pregnancy test result or a missed menstrual period.

A test may show that you're pregnant because it detects a hormone called human chorionic gonadotropin (HCG). The body starts to make this pregnancy hormone when the fertilized egg attaches to the wall of the uterus. Then HCG is released by cells in the placenta, the organ that forms during pregnancy to deliver nutrients and oxygen to an unborn baby. The placenta briefly begins to form during an anembryonic pregnancy.

You may have symptoms of early pregnancy, such as tender breasts, upset stomach and vomiting. But when the embryo stops growing and hormone levels fall, pregnancy symptoms often fade.

At this point, you might have mild cramping or pelvic pain and light spotting or bleeding from the vagina. An ultrasound of the uterus will show an empty fluid-filled structure, called a gestational sac, with no embryo inside it. In healthy pregnancies the sac surrounds an embryo.

An anembryonic pregnancy leads to a miscarriage. Some people choose to wait for the miscarriage to happen naturally. Others take medicine to trigger it. In some cases, a procedure called dilation and curettage is used to suction pregnancy-related tissues from the uterus.

Most people who've had an anembryonic pregnancy go on to have successful pregnancies. If you have two or more miscarriages in a row, talk with your doctor or other health care professional to find any underlying causes.

• Miscarriage and stress