A blighted ovum occurs when a fertilized egg implants in the uterus but doesn't develop into an embryo. It is also referred to as an anembryonic pregnancy and is a leading cause of early pregnancy failure or miscarriage. Often it occurs so early that you don't even know you are pregnant.
A blighted ovum causes about one out of two miscarriages in the first trimester of pregnancy. A miscarriage is when a pregnancy ends on its own within the first 20 weeks.
When a woman becomes pregnant, the fertilized egg attaches to the uterine wall. At about five to six weeks of pregnancy, an embryo should be present. At about this time, the gestational sac -- where the fetus develops -- is about 18 millimeters wide. With a blighted ovum, though, the pregnancy sac forms and grows, but the embryo does not develop. That's why a blighted ovum is also called an anembryonic pregnancy.
What Causes a Blighted Ovum?
Miscarriages from a blighted ovum are often due to problems with chromosomes, the structures that carry genes. This may be from a poor-quality sperm or egg. Or, it may occur due to abnormal cell division. Regardless, your body stops the pregnancy because it recognizes this abnormality.
It's important to understand that you have done nothing to cause this miscarriage and you almost certainly could not have prevented it. For most women, a blighted ovum occurs only once.
Signs of a Blighted Ovum
With a blighted ovum, you may have experienced signs of pregnancy. For example, you may have had a positive pregnancy test or a missed period.
Then you may have signs of a miscarriage, such as:
- Abdominal cramps
- Vaginal spotting or bleeding
- A period that is heavier than usual.
If you're experiencing any of these signs or symptoms, you may be having a miscarriage. But not all bleeding in the first trimester ends in miscarriage. So be sure to see your doctor right away if you have any of these signs.
Diagnosing a Blighted Ovum
If you thought you had a normal pregnancy, you're not alone; many women with a blighted ovum think so because their levels of human chorionic gonadotropin (hCG) may increase. The placenta produces this hormone after implantation. With a blighted ovum, hCG can continue to rise because the placenta may grow for a brief time, even when an embryo is not present.
For this reason, an ultrasound test is usually needed to diagnose a blighted ovum -- to confirm that the pregnancy sac is empty.