WHAT IS VANISHING TWIN SYNDROME? CAUSES, SYMPTOMS, AND MANAGEMENT
Medically Reviewed by Dr. Sony Sherpa (MBBS)
Vanishing Twin Syndrome (VTS) is a possible occurrence in multiple pregnancies where one of the fetuses is lost in the first trimester[1]. The mother's body, the surviving twin(s), or the placenta then reabsorb the tissue of the vanished twin. This condition often went undetected before the widespread use of ultrasound in early pregnancy.[2]
VTS is surprisingly common. It is estimated to occur in 20-30% of all multiple pregnancies[3].
While the surviving twin usually goes on to have a healthy pregnancy and birth, it is essential for the parents to understand the causes, symptoms, and management of VTS.
What Causes Vanishing Twin Syndrome?
The cause of VTS is not fully understood, and the phenomenon remains understudied. Researchers theorize that similar to a miscarriage, this is likely the result of sporadic mutations, either inherent in the vanishing twin, occurring sporadically due to environmental exposures, or arising in the placenta. Gene mutations are usually seen in the vanishing fetus.
What Are the Risk Factors for VTS?
While VTS can occur in any pregnancy, certain risk factors may increase the likelihood of its occurrence. These include:
- Advanced maternal age: Women over the age of 30 have a higher risk of VTS.
- Previous history of VTS: Women who have experienced VTS in an earlier pregnancy have a higher risk of it occurring again.
- Miscarriage: Recurrent pregnancy losses share a link with future miscarriage[4] due to gene mutations, which may potentially result in vanishing twin syndrome during multiple pregnancies.
- ART and IVF fertility treatment: The use of assisted reproductive technology (ART) and in vitro fertilization (IVF) can elevate the likelihood of having a multiple pregnancy, which in turn increases the risk of VTS. Common complications of IVF-related VTS include premature birth and low birth weight[5].
- Nutrient deficiencies: Some deficiencies, such as folate, are implicated in miscarriage and congenital deformities. While it is not clear whether deficiency plays a role in VTS, it is protective for the mother to support gestation with optimal supplementation.
What Are the Symptoms of Vanishing Twin Syndrome?
The most common symptom of VTS is the disappearance of one of the fetuses during the first trimester. This can be detected through ultrasound scans, where the presence of a gestational sac without a fetal pole or heartbeat may indicate the loss of one of the fetuses.
Other symptoms do not frequently occur during pregnancy, and VTS does not pose any significant risk to the surviving twin or the mother. In rare cases, the expectant mother may also experience[6]:
- Low hCG levels: In some cases, human chorionic gonadotropin (hCG) levels fall lower than expected for a multiple pregnancy.
- Bleeding: Some women may experience light bleeding or spotting during the first trimester, which may be a sign of VTS.
Is Vanishing Twin Syndrome a Miscarriage?
VTS is sometimes thought of as a type of partial miscarriage. However, in VTS, a surviving twin continues to grow and develop normally, while in a miscarriage, the loss comprises the entire pregnancy.
Complications
In most cases, VTS poses no significant complications for the mother. However, in rare cases, complications can include:
- Incomplete resorption: In some cases, the mother’s body only absorbs a portion of the tissue of the lost fetus, which can lead to complications such as infection.
- Risk of infection: Incomplete resorption can increase the risk of infection for the mother.
- Miscarriage or Premature Birth: An expectant mother with VTS may have a weakened cervix (cervical insufficiency), leading to premature birth or pregnancy loss in the surviving twin.
- Hemorrhaging: Bleeding due to VTS is common if the twin vanishes later on during gestation and can lead to miscarriage of the surviving twin.
- Psychological impact: VTS may be a cause for depression for some mothers, especially if the pregnancy ends in miscarriage.
How is the Surviving Twin Affected?
In most cases, the surviving twin does not suffer any complications as a result of losing their twin in the womb. They continue to grow and develop normally, and the pregnancy progresses as a singleton pregnancy.
In rare instances, the surviving twin suffers from the following complications:
- Cerebral palsy[7]
- Premature rupture of membranes of the surviving fetus, leading to miscarriage or severe birth complications (associated with twin transfusion syndrome).
- Intrauterine growth restriction (IUGR), where one or both fetuses are not growing at a standard rate, causing a low birth weight, microcephaly, or stunted development.[8]
- A low Apgar score[9], indicates potential complications at birth, including breathing, heart rate, muscle tone, reflexes, and skin color, which may require immediate medical attention.
- A benign teratoma tumor arising from leftover matter from the vanishing twin.
In rare instances, the surviving baby may absorb some cells from the vanished twin. This results in the surviving baby becoming an illusion, an individual with two distinct sets of DNA.
Some research reveals that VTS may increase the risk of cognitive impairment, potentially leading to neurodevelopmental delays in the survivor twins. However, more research is necessary to confirm this observation.
How is VTS Diagnosed?
In early pregnancy, VTS frequently goes unnoticed. The embryo may vanish before any observable symptoms occur, and without early detection, medical professionals can overlook the initial presence of multiple fetuses.
VTS is diagnosable through ultrasound scans during routine prenatal checkups between weeks 8 and 12 of pregnancy[10]. Fetal disappearances are detectable through the absence of a fetal pole or heartbeat in the gestational sac. In some cases, the surviving twin may also show signs of stunted growth or other complications, which may prompt further testing.
If a twin perishes after the embryonic stage of development, the water within its tissues, as well as the amniotic fluid and placental tissue may be absorbed. This process can lead to the deceased twin being compressed under the pressure exerted by the surviving twin(s), resulting in a flattened appearance.
Upon delivery, there are two ways to identify this:
- Fetus Compressus: The deceased fetus is noticeably compressed.
- Fetus Papyraceous: The deceased fetus is remarkably flattened, having lost most of its fluid and soft tissue.
Your doctor may also track your levels of human chorionic gonadotropin (hCG). This is a hormone that signifies that pregnancy is underway in the mother’s body, and its levels can explain the pregnancy's progress. If hCG levels plateau or decline despite an initially suspected multiple pregnancy, it could be a sign of VTS.
How is VTS Managed?
In most cases, VTS does not require any specific treatment or management. The pregnancy can continue as a singleton pregnancy in which the mother and surviving twin attend routine checkups to monitor for any potential complications.
However, in some cases, there may be a need for additional monitoring and management, such as:
- Treatment for IUGR: If the surviving twin is experiencing intrauterine growth restriction, they may require additional monitoring and treatment to ensure proper growth and development. Management of IUGR depends on the cause, yet bed rest is a standard recommendation alongside adequate supplementation.[11]
- Monitoring of hCG levels: In some cases, it is necessary for a healthcare team to monitor hCG levels.
- Management of complications: If there are any complications associated with VTS, such as cervical insufficiency or gestational diabetes, they may require suitable management.
- Psychosocial support: Social support from family and friends is essential during this time to help the mother cope. If the experience is too distressing, psychotherapy may help.
Is a D&C necessary for VTS?
A dilation and curettage (D&C) procedure is a standard miscarriage protocol that involves removing uterine tissue to diagnose or treat various gynecological conditions, especially miscarriages[12].
While sometimes considered for treating VTS complications, it is not necessary in most cases. Reasons for this include:
- The body typically reabsorbs the tissue of the vanished twin without intervention.
- VTS often occurs early in pregnancy, allowing for complete resorption before significant tissue develops.
- If VTS happens in the first trimester, the risks of complications like infection or excessive bleeding are generally low.
- A D&C procedure carries its potential risks, including infection, damage to the cervix, or uterine perforation.
There are some circumstances where a doctor might recommend a D&C after VTS:
- Incomplete Resorption: If a significant amount of tissue remains from the vanished twin, it can sometimes lead to bleeding or infection.
- Concerns about Incomplete Resorption: In some cases, the doctor may need clarification on whether the resorption will be complete and suggest a D&C to prevent potential complications.
Confer with your healthcare provider in order to decide whether a D&C is suitable after VTS. They will carefully consider your situation, the stage of pregnancy, and any potential risks before making a recommendation.
Dealing with Vanishing Twin Syndrome
For those who have experienced VTS, it can be a difficult and emotional experience. Seeking support and talking to a healthcare professional if needed is important. It may help to choose to honor the lost twin in a way that seems appropriate without losing sight of the developing survivor twin.
Latest Advancements in VTS Research
Researchers are continuously investigating vanishing twin syndrome and its potential underlying causes.
The latest advances pertain to improved diagnostic measures:
- Improved Ultrasound Technology: Ultrasound technology continually advances, leading to higher-resolution images and more precise measurements. AI integration allows for dramatic improvements to the quality of prenatal ultrasound imaging.[13]
- Genetic Screening: If researchers pinpoint specific gene mutations that give rise to VTS, future genetic screening may become available, allowing potential parents to assess their risk. Tests are under development that can identify VTS based on single gene mutations.[14]
Conclusion
Vanishing Twin Syndrome (VTS) is a rare occurrence in pregnancy in which one of the fetuses in a multiple pregnancy is lost in the first trimester. While the surviving twin usually goes on to have a healthy pregnancy and birth, it is crucial to comprehend the causes, symptoms, and management of VTS. With advancements in research, we can continue to learn more about this condition and support those who have experienced it.
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