What Is the Empty Sac in Pregnancy? - Blighted Ovum Causes & Treatments


An anembryonic pregnancy, also known as a blighted ovum, is a type of miscarriage that occurs when a fertilized egg implants in the uterus but fails to develop into an embryo. Instead, the placenta grows abnormally, forming a mass of cysts. Despite the absence of an embryo, the placenta continues to produce the hormone human chorionic gonadotropin (HCG), resulting in positive pregnancy test results. However, an ultrasound will reveal an empty gestational sac without an embryo.

During an anembryonic pregnancy, the gestational sac and placenta continue to develop, but the embryo does not form within the sac. This condition typically leads to a miscarriage in the first trimester of pregnancy. In most cases, the mother's body may detect chromosomal abnormalities in the fertilized egg and naturally miscarry.

A blighted ovum can sometimes present with no symptoms and may only be detected during a routine ultrasound. However, some women may experience severe nausea and vomiting, particularly those with a history of miscarriage or anembryonic pregnancy and women over 40 years old.

In this article, we will explore the causes and symptoms of anembryonic pregnancy, as well as the risk factors associated with this condition.

Blighted Ovum

What Is an Anembryonic Pregnancy, and How Does It Occur?

When a sperm fertilizes an egg, the resulting embryo should begin to develop and grow. However, in the case of an anembryonic pregnancy, there is a disruption in this process, and the embryo fails to form. Despite the absence of an embryo, the placenta continues to grow and produce the hormone human chorionic gonadotropin (hCG), leading to positive pregnancy test results. 

A blighted ovum commonly occurs in the first trimester of pregnancy, characterized by the absence of a developing embryo within the gestational sac. An ultrasound is often the only way to detect an empty gestational sac.

The placenta continues to grow without the embryo, causing the pregnancy hormone levels to rise, making the mother feel pregnant. However, the mother's body usually recognizes that there is a problem and miscarries the empty gestational sac. This process is often referred to as a "silent miscarriage" because there may be no symptoms of a miscarriage, such as bleeding or cramping.

As the growth of the placenta stops and hormonal levels decrease, pregnancy symptoms also lessen. In such cases, women may experience mild cramping, spotting, and light bleeding. 

It's important to note that the gestational sac is a fluid-filled structure that develops in the uterus early in pregnancy. It surrounds the embryo and provides a protective environment for its growth and development.

What Are the Symptoms of a Blighted Ovum?

Even though a blighted ovum may present with signs and symptoms resembling a normal pregnancy, it may also have specific symptoms that can vary in severity from patient to patient.

These symptoms may include:

  • Severe nausea and vomiting;
  • Dark or light brown vaginal bleeding within the first three months of pregnancy;
  • Pelvic and lower abdominal cramping and pain (rare);
  • Absence of fetal heartbeat;
  • Thyroid disease such as hyperthyroidism;
  • High levels of HCG hormone;
  • High blood pressure or primary preeclampsia
  • High protein levels in urine after at 20th week;
  • Anemia;
  • Ovarian cysts;
  • Rapid and excessive growth of the uterus;
  • Grape-like cysts Coming out of the vagina;
  • Pregnancy poisoning (preeclampsia).


What Are the Symptoms of a Blighted Ovum?

Does the Beta HCG Level Rise with a Blighted Ovum?

In a normal pregnancy, the beta hCG level increases as expected. With a blighted ovum, the beta hCG level can continue to rise because the placenta may grow quickly, even though there is no embryo. For this reason, an ultrasound test is typically needed to diagnose a blighted ovum - and to confirm that the pregnancy sac is empty.

When Do the Symptoms of a Blighted Ovum Begin?

The symptoms of a Blighted Ovum may usually be visible between the 8th and 13th weeks of pregnancy. It is often identified by an ultrasound, which employs sound waves to examine the placenta and observe the empty sac on the sonogram screen. 

To diagnose an anembryonic pregnancy, the doctor will perform an ultrasound to determine the empty gestational sac with no sign of an embryo at 6 to 8 weeks of pregnancy. However, the confirmation of a blighted ovum depends on accurate calculation of the pregnancy age and conducting an ultrasound after the 5th week. If not, the doctor will schedule a follow-up ultrasound in one to two weeks. 

Typically, the fetal heartbeat can be heard at week 8 of pregnancy, so the absence of fetal heartbeat confirms an anembryonic pregnancy.

What Causes an Anembryonic Pregnancy?

The exact cause of a blighted ovum is not always clear, but several factors may contribute to this condition:

Blighted ovum miscarriages are primarily caused by issues with chromosomes, the structures that carry genes. In this case, the mother’s body stops the pregnancy as it recognizes these abnormalities. 

A blighted ovum can also result from a low-quality sperm or egg or abnormal cell division. In this case, the body will not be able to recognize the empty gestational sac. It is because the pregnancy hormones are being secreted, and this can prevent miscarriages. This can happen to anyone.

The common causes of an Anembryonic Pregnancy are:

  • Previous miscarriage;
  • past a blighted ovum;
  • Advanced maternal age, particularly being over 40 years old;
  • family history of genetic disorders; 
  • Manganese superoxide dismutase (MnSOD) gene.


Causes an Anembryonic Pregnancy

How to Diagnose an Anembryonic Pregnancy?

An ultrasound is the primary method for diagnosing an anembryonic pregnancy that is typically performed between 6-9 weeks of gestation to visualize the contents of the uterus. 

During an ultrasound, the size of the gestational sac is measured. If the diameter of the sac is greater than 20 mm, but no fetus is visible inside it, this indicates that an anembryonic pregnancy has occurred. If the diameter of the gestational sac measures less than 20 mm during an ultrasound, it indicates it is still early in the pregnancy. In this case, the ultrasound should be repeated after two weeks to allow for further embryo development and to confirm a viable pregnancy.

It is also worth mentioning that after the confirmation of an anembryonic pregnancy, the doctor may also conduct examinations for conditions like hyperthyroidism, preeclampsia, and anemia.

What Is the Difference Between Anembryonic Pregnancy vs Molar Pregnancy?

The key differences between anembryonic pregnancy and molar pregnancy lie in their abnormal development, underlying causes, and aftercare. Anembryonic pregnancy pertains to a situation where the gestational sac does not contain an embryo. At the same time, molar pregnancy (also called Hydatiform mole or HM) involves anomalous growth of placental tissue, with or without abnormal fetal development.

In addition, it is recommended to use contraception for three months after an anembryonic pregnancy before trying to conceive again. However, in the case of a miscarriage due to a molar pregnancy, continuous medical monitoring is necessary for an extended period, and the interval before attempting another pregnancy will be substantially longer.

What Size Is the Anembryonic Gestational Sac?

By the 6th week of a typical pregnancy, the fetus becomes visible inside the gestational sac, measuring around 18mm in diameter. However, in a blighted ovum, the gestational sac develops normally, but the embryo does not form or stops developing very early. Therefore, the ultrasound will confirm the blighted ovum if the gestational sac diameter is 4 mm but without an embryo inside, 

Ultrasound is typically used to measure the diameter of the gestational sac. 

  • A pregnancy is anembryonic if a transvaginal ultrasound reveals a sac with a mean gestational sac diameter (MGD) of more than 25 mm and no yolk sac;
  • Pregnancy is early if a transvaginal ultrasound reveals a sac with a mean gestational sac diameter (MGD) less than 25 mm. In this case, the ultrasound should be repeated in one to two weeks.


What Size Is the Anembryonic Gestational Sac?

How Is a Blighted Ovum Removed?

In the case of an anembryonic pregnancy, the decision of whether to have a dilation and curettage (D&C) or wait for a natural miscarriage depends on individual circumstances. 

During an ultrasound, the size of the pregnancy sac is measured, and the presence of an embryo or yolk sac is checked. If the sac is larger than 20 mm but there is no embryo, it is diagnosed as an anembryonic pregnancy. It is important to examine the entire sac using a vaginal ultrasound thoroughly.

If the sac is smaller than 20 mm, it indicates that the pregnancy has not progressed significantly. In such cases, a follow-up ultrasound is typically scheduled for two weeks later. An anembryonic pregnancy eventually leads to a miscarriage.

When the levels of pregnancy hormones start to decrease, it indicates that the body will naturally expel the pregnancy tissue. However, this process may take several weeks. Medication or a D&C procedure may be used to remove the placenta in certain situations. 

It is important to note that D&C is not usually recommended for a first pregnancy, as the body is capable of naturally eliminating the fetal tissue. The use of D&C is typically only necessary if the individual wants to conduct a tissue pathology test to investigate the cause of the miscarriage.

How Is a Blighted Ovum Removed?

How to Prevent an Anembryonic Pregnancy?

Unfortunately, there is no guaranteed way to prevent an anembryonic pregnancy. This type of miscarriage rarely occurs more than once. When the miscarriage happens, menstruation resumes and the individual can attempt to conceive again.

However, it is advisable to wait for at least 12 menstrual cycles before attempting a second pregnancy, allowing the body adequate time to recover. In the case of recurrent miscarriages, it is essential to consult a gynecologist to detect the underlying cause. Moreover, undergoing genetic testing before pregnancy can help reduce the risk of a blighted ovum.

Final Word

Anembryonic pregnancy, also known as a blighted ovum, is a condition wherein a fertilized egg implants in the uterus but fails to develop an embryo. Although this condition can be emotionally devastating for expectant parents, understanding the causes, symptoms, and treatment options can help mitigate the anxiety and provide necessary support. 

Early detection through ultrasound and hormonal monitoring is crucial for accurate diagnosis, allowing doctors to determine the most appropriate course of action. 

Frequently Asked Questions about a Blighted Ovum

1) How to know if my pregnancy is anembryonic?

As mentioned, an ultrasound can reveal the condition. Complication. In the early stages of pregnancy, it is common for an empty sac to be detected due to the inability to visualize the embryo at that point. However, an embryo should be visible within the sac on ultrasound with progressing gestational age. If an empty gestational sac persists beyond a certain gestational age (usually around 7-8 weeks), it could indicate the presence of a blighted ovum.

2) Why is there no embryo in an anembryonic pregnancy?

This usually happens due to advanced maternal age, chromosomal abnormalities, or genetic issues with the fertilized egg. In some cases, there may be an issue with the quality of the sperm or egg that prevents proper development. These abnormalities prevent the early embryonic development and the formation of an embryo.

3) Who is at a higher risk of experiencing anembryonic pregnancy?

Women under the age of 20 or over 35, as well as those with a history of previous blighted ovum, may have a higher risk of experiencing it. 

4) Is it possible to get pregnant after an anembryonic pregnancy?

It is typically possible to have a successful pregnancy following a blighted ovum. However, it is advisable to wait for a period of 6 to 12 months before attempting to conceive again and to seek the guidance of a doctor throughout the next pregnancy.

5) Can an anembryonic pregnancy be successful? 

No, an anembryonic pregnancy cannot succeed. It occurs when a fertilized egg implants and begins to develop, but the embryo does not develop or is not present. In such cases, only the gestational sac develops, and the pregnancy cannot progress further.

Despite presenting symptoms similar to a normal pregnancy during its initial stages, a blighted ovum triggers the mother's body to identify irregularities and halt the pregnancy process. If spotting and abdominal pains arise after pregnancy symptoms, it is possible to detect the presence of an anembryonic pregnancy. This condition may result in a natural miscarriage or necessitate medical interventions to bring it to a conclusion.

6) Is it possible to experience recurrent blighted ovum?

Based on experience, women typically experience the blighted ovum only once. The chances of experiencing Recurrent Blighted Ovum are low, ranging from 1-2%. Therefore, some may argue that investigating the condition's underlying cause is unnecessary. 

However, considering that genetic disorders are known to be the primary cause of blighted ovum, it is necessary for patients to take specific tests to enhance their chances of a successful subsequent pregnancy.

7) At what stage does a blighted ovum usually miscarry?

In most cases, the blighted ovum will miscarry naturally, usually in the first trimester of pregnancy before 20 weeks. However, the abortion timing can increase in cases where a woman is unaware of their anembryonic pregnancy and has not sought medical advice for an extended period.

8) What is an empty gestational sac?

The gestational sac is a fluid-filled structure that forms within the uterus around the fourth to fifth week of fertilization and surrounds the placenta, yolk sac, and embryo. However, the absence of the yolk sac in the gestational sac indicates the absence of an embryo, yet the women experience unmistakable signs of pregnancy. 

This condition is referred to as a blighted ovum that may often lead to natural miscarriage during the first trimester.

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