An anembryonic pregnancy occurs when a gestational sac forms, but an embryo fails to develop. This condition is also called a blighted ovum, though this term is not as widely used because it is not as descriptive. The exact number of anembryonic pregnancies that occur is unknown, but it is estimated to be the cause of about half of all miscarriages that occur in the first trimester.
The cause of anembryonic pregnancy is difficult to determine and is often studied, along with embryonic pregnancies, when looking at early pregnancy loss. Possible embryonic abnormalities can result in a blighted ovum, the most common being chromosomal abnormalities. There is also a connection between sperm with DNA damage and miscarriage in early pregnancy.
Maternal factors may also contribute to anembryonic pregnancy, including obesity, advanced maternal age, genital tract infections, malformation of the uterus, and immunologic disorders. Hormonal factors, such as low progesterone levels and thyroid dysfunction, can also be at play. Experts have linked polycystic ovary disease to early pregnancy loss, but it is difficult to determine which type — embryonic or anembryonic — it causes.
Because there is no identifiable cause for anembryonic pregnancy, risk factors are hard to identify. Maternal age has a lot of impact on early pregnancy loss. Research shows that only 10 percent of women between 20 and 24 years of age experience early pregnancy loss. For women 40 to 44, this figure increases dramatically, to 51 percent.
Anembryonic pregnancy occurs very early, so early that some women may not even know they are pregnant. Others may have symptoms of early pregnancy, including a late or missed period and a positive pregnancy test. In the case of a blighted ovum, the placenta continues to grow and pregnancy hormones continue to rise, suggesting the pregnancy is on track, though the woman may experience cramping and spotting or bleeding.
Diagnosis usually does not occur until an ultrasound exam reveals an empty gestational sack. The doctor will officially issue the diagnosis when they find no embryo in a gestational sac with a diameter of 25 mm or greater. A yolk sac may be present in some cases. The doctor may perform follow-up scans to confirm.
Eventually, anembryonic pregnancies end in miscarriage. After diagnosis, the woman and her doctor discuss options for proceeding. The doctor may recommend dilation and curettage, a brief surgical procedure where the cervix is dilated, and the uterine lining is scraped to remove any remaining tissue from the pregnancy. This is not often necessary because the woman's body is usually capable of passing the tissue, but a D&C does allow a pathologist to analyze the tissue and attempt to determine the cause of the miscarriage.
There are multiple ways to proceed with anembryonic pregnancy, and the decision should be left up to the woman and her doctor. Since a blighted ovum eventually results in miscarriage, some women choose a watchful waiting approach, allowing the body to expel the tissue naturally and following up with the doctor for tests to make sure all the tissue has passed. Medical management involves a vaginal suppository to encourage the body to expel the tissue, and surgical treatment may be needed if the woman experiences blood pressure issues.
After anembryonic pregnancy, prognosis is good, regardless of which management option the woman chooses. While some women prefer watchful waiting as a more natural option, studies show that medical management is more successful. When surgical treatment is necessary, it has a high success rate and is generally safe.
Anembryonic pregnancy is quite common, particularly in early pregnancy, which is defined as before 13 weeks gestation. Researchers believe that between 15 and 20 percent of all pregnancies end in miscarriage. Of those that occur in the first trimester, 50 percent of them are believed to be caused by a blighted ovum.
Most women who experience a blighted ovum or anembryonic pregnancy have subsequent successful pregnancies. This is true even when the cause of the blighted ovum is undetermined. That said, women who experience multiple miscarriages should talk to their doctor to try to determine the underlying cause.
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