What Causes a Blighted Ovum?

Miscarriage from a blighted ovum is usually caused by genetic chromosomal defects in the fertilized ovum, according to WebMD. A blighted ovum is a fertilized egg that implants in the uterus, but then fails to develop into an embryo.

Also referred to as an anembryonic pregnancy, because the gestational sac develops but the embryo does not, blighted ovum causes half of all miscarriages during the first trimester, states WebMD. The Mayo Clinic explains that a blighted ovum usually occurs in the first few weeks of pregnancy, frequently before a woman knows she is pregnant.

A woman with an anembryonic pregnancy can miss a period or get a positive result from a pregnancy test, because the placenta releases a pregnancy hormone called human chorionic gonadotropin or HCG, states the Mayo Clinic. When the embryo fails to develop, the placenta stops growing and the pregnancy hormone subsides. Eventually a miscarriage occurs.

WebMD explains that the pregnancy fails because either the egg or sperm contributed damaged chromosomes or because the fertilized egg's cells fail to divide properly. The woman's body stops the pregnancy because it recognizes the abnormality.

If a woman has one blighted ovum that does not mean that she will necessarily have another. The Mayo Clinic states that most women who experience a blighted ovum go on to have successful pregnancies.