Anembryonic pregnancy, anembryonic gestation or early embryonic demise, commonly referred to as blighted ovum or just embryo loss, is one of the most common causes of miscarriage. Nearly 50% of all cases of pregnancy loss during the first trimester occur as a consequence of a blighted ovum, often before the woman is even aware that she is pregnant.
The different sections of this article have been assembled into the following table of contents.
What does anembryonic pregnancy mean?
An anembryonic gestation is a pregnancy that is clinically recognized, but the gestational sac appears empty on the ultrasound, without signs that there's a developing embryo inside.
In cases of anembryonic pregnancy, fertilization has taken place, that is, the sperm has met the egg. However, when the embryo attaches to the uterine lining, its development occurs abnormally, and leads to an empty gestational sac. To put it simply, it's like a developing pregnancy without a baby.
It is called blighted ovum when no embryonic structures can be seen inside the gestational sac, that is, when it appears empty on the ultrasound scan.
Normal embryo development
Right after the sperm meets the egg, an embryo starts developing. From this moment on, the embryo cells will divide until it reaches the blastocyst stage. A blastocyst embryo is composed of an outer layer of cells that form what is called trophoblast. At the same time, it surrounds the inner cell mass as well.
When the blastocyst embryo attaches to the uterus, the trophoblast will give rise to the placenta, and the inner cell mass will develop into the embryonic disks that form the fetus. This process is known as gastrulation.
What causes an anembryonic pregnancy?
When the cells that form the embryonic disks do not develop as they should, cell specialization and tissue formation never occur. This phenomenon is what we call blighted ovum. This causes the cell layers of the gestational sac to continue growing indefinitely and secreting human chorionic gonadotripin (hCG). This is the reason why you can still get a positive pregnancy test despite the absence of a developing embryo.
80% of the cases of anembryonic pregnancy are caused by chromosomal abnormalities in either the egg cell or the sperm cell, which generate an error in coding after fertilization. The consequence is a very early pregnancy loss.
Another possible cause is an abnormal cell division in the embryo right after fertilization occurs.
The diagnosis of a blighted ovum is done by ultrasound, when the specialist sees an empty sac. If this happens, another ultrasound will be scheduled for the following week to confirm the presence or not of an embryo and, if so, the fetal heartbeat.
Pregnancy can be detected at different stages. If no embryo is seen in any of these phases, it may be a case of anembryonic pregnancy:
- The gestational sac is the first embryonic structure that can be seen via ultrasound scan, approximately on the 4th-5th week of pregnancy.
- The yolk sac or fetal pole is an embryonic structure that is located inside the gestational sac, and can be observed by ultrasound on days 2 or 3 after seeing the embryo for the first time.
- Around weeks 7 to 12 of pregnancy, it's possible to hear the fetal heartbeat by doppler ultrasound.
- Finally, the fact that the yolk sac can be seen through ultrasound confirms that the woman is pregnant.
Being unable to see the fetal pole is an indicator of anembryonic pregnancy.
In addition to an ultrasound scan, the absence of pregnancy symptoms and the hormonal levels of the woman will be clear indicators of an anembryonic pregnancy. If the hormonal levels start diminishing, it means that an early pregnancy loss has occurred.
When an anembryonic pregnancy occurs, the woman still tests positive for pregnancy because this hormone is produced by the cell layers of the gestational sac, even if it is actually empty.
The main side effect of an anembryonic pregnancy is the termination of pregnancy, either by means of:
- Spontaneous abortion or miscarriage, accompanied by a natural expulsion and vaginal bleeding.
- D&C after a diagnosis by ultrasound.
Once the absence of embryonic structures has been detected, there is no reason for an empty gestational sac to remain inside the woman's uterus, as the cells end up degenerating and the toxic substances that they produce can lead to serious health conditions. Unfortunately, a miscarriage is the only possible solution, with the subsequent genetic examination of the tissue that has been removed.
It is likely that the woman doesn't even know that she has had an anembryonic pregnancy, as it is possible for the miscarriage to be confused with the menstruation.
What is the recurrence rate?
The fact that an anembryonic pregnancy has occurred once does not mean that you are at risk of going through a second one in the future, neither that you are going to have fertility issues.
This type of miscarriage, provided that it progresses normally, should not lead to reproductive complications in the future. The patient will be able to become pregnant again without problems after receiving the appropriate treatment in the future.
In case it was recurrent, the most recommendable is to carry a genetic study of the couple to determine the cause the is preventing embryo development.
FAQs from users
Will I be able to get pregnant again after a blighted ovum?
An anembryonic pregnancy is not linked to infertility. In principle, you will be able to get pregnant again as soon as you begin ovulating.
When does miscarriage happen with a blighted ovum?
It often occurs so early that you don't even know you were pregnant. It often occurs within the first 20 weeks of pregnancy.
Suggested for you
If you want to learn more about the types of miscarriage and their causes, aside from the one explained here, you can continue reading here: Types of Miscarriage.
To learn more about fetal development an the changes that occur both in the mother and the fetus, check the following post out: Pregnancy Stages by Month.
We have made reference to ultrasound imaging (sonography) as a technique for confirming a pregnancy. Learn more about it here: What Is a Fetal Ultrasound?
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