Vanishing Twin Syndrome: Causes, Symptoms & Treatment

Twin pregnancies, although exciting, are often associated with pregnancy and delivery-related complications. Vanishing twin syndrome is one such complication which involves the loss of one of the multiple gestation.

What is Vanishing Twin Syndrome?

This is described as a condition seen in a multiple pregnancy in which one (or more than one in a triplet or quadruplet pregnancy) foetus happens to disappear intra-uterine before birth. It is assumed that the wasted foetal tissues are taken up either by the placenta or the other twin for nutrition.

How Common is Vanishing Twin Syndrome?

As per reports, multiple gestation occurs at a frequency of 3 to 5 per 100 pregnancies. The statistics of vanishing twin syndrome suggest that about 20-25% of these multiple pregnancies witness the phenomenon of vanishing twin syndrome. The data related to pregnancies and childbirth from European countries suggests that among every 100 babies born with assisted reported techniques (ART), around 15-20 are twin gestations.

Occurring early in the first trimester, this syndrome rarely causes any complication in the mother besides subtle abdominal cramping/pain and PV bleeds (vaginal bleeding).

Vanishing twin syndrome occurring in later pregnancy may cause complications like premature delivery, sepsis due to the retained products of conception, excessive bleeding, coagulopathies (inability of the blood to clot), and an increased risk of disseminated intravascular coagulation (creation of blood clots in the small blood cells). The foetal remnants, if low-lying in the uterine outlet, may cause an obstructed labour and might require assisted surgical delivery or caesarian section.

Besides mortality of the vanishing twin, it may also affect the well-being of the other twin by causing neurological problems like cerebral palsy or skin problems, like aplasia cutis (absence of skin).

Who is At The Risk of Getting Vanishing Twin Syndrome?

Studies suggest that maternal age is associated with vanishing twin syndrome. Increased maternal age (more than 30-35 years) often requires assisted reproductive techniques (ART) which in turn increases the probability of multiple gestations. Vanishing twin syndrome, as already described, occurs in multiple pregnancies with a frequency of 20-25 percent.

Causes of Vanishing Twin Syndrome

Why does the vanishing twin syndrome happen? The exact causes of vanishing twin syndrome largely remain undescribed. Placental tissues after birth of the healthy twin have been studied in detail. It is observed that the main reasons for the demise of one of the twins are developmental malformations and chromosomal anomalies, both largely genetic in nature. The other twin is usually healthy and unaffected. Placental conditions, in some cases, may also be the cause of foetal demise.

Signs and Symptoms

Vanishing twin syndrome in early pregnancy may be totally asymptomatic for the mother. In later pregnancy, it may cause symptoms similar to those of miscarriages. These include symptoms like:

• Abdominal cramps
• Bleeding through the vagina
• Dull pain in the pelvic region
• Routine blood tests may show a reduced level of Beta-HCG or the pregnancy hormone. It is secreted by the placenta and is usually tested to exclude conditions like vesicular mole.

These symptoms are non-specific and may only suggest a possibility of vanishing twin syndrome. You must consult your clinician if you experience any of these symptoms.

How Frequently Does the Vanishing Twin Syndrome Happen?

Vanishing twin syndrome is associated with multiple pregnancies which are quite common nowadays owing to the availability of assisted reproductive techniques. As discussed, it is estimated to occur at a rate of 20-30 per 100 multiple pregnancy cases.

Risks and Effects on Mother and Surviving Twin

The complications of vanishing twin syndrome are rare for the mother and the surviving twin if it occurs early (during the first trimester of pregnancy). However, the cause of foetal mortality may have an impact on the pregnancy outcome.

If it occurs during the second or third trimester, the other foetus is at a higher risk of having developmental problems including cerebral palsy.

Death of a twin during the embryonic phase may significantly reduce the amniotic fluid and cause the placenta to shrink in size. The living twin exerts pressure which causes structural changes in the dead foetal tissue. During delivery, the dead foetus may appear significantly compressed. This is known as foetus compressus. It could also be notably flattened due to the reduced amniotic fluid and placental shrinkage. This is known as foetus papyraceous.

Diagnosis

A diagnosis of vanishing twin syndrome is often made before it gets clear that the mother was actually carrying twins. An ultrasound examination confirms the diagnosis of a vanishing twin. It shows the presence of an embryonic sac with incompletely developed foetal parts, or by the absence of foetal cardiac motion in one of the two foetal masses (vanishing twin syndrome ultrasound diagnosis). When multiple gestation is confirmed, a blood test for beta HCG may also help diagnose vanishing twin syndrome. However, vanishing twin radiology is the only confirmatory and preferred investigation for diagnosis.

Treatment

No specific treatment is required for vanishing twin syndrome detected in early trimester of pregnancy, as long as the mother and living twin have stable blood flow. However, regular monitoring of the surviving foetus is advisable. If the surviving twin is healthy and scans show no abnormalities, there are good chances of a normal, uneventful pregnancy with the delivery of a single, healthy baby.

In cases diagnosed later (in second or third trimesters), the plan of treatment is largely based on the duration of pregnancy, developmental profile, and chorionic pattern of the living foetus. The twins could have either been monochorionic (shared chorionic and amniotic sac) or dichorionic (separate chorionic and amniotic sacs). Dichorionic twin gestations with either twin vanishing are generally safe for the other and require no intervention. However, the death of a monochorionic twin is an indication of urgent delivery of the other twin, provided it has attained lung maturity or crossed 32 weeks of gestation. The benefits of delivering the living baby should outweigh the risks of perinatal complications. In cases where delivery is not possible or advisable, the living foetus should be closely monitored for any intra uterine complications.

A recent advancement in the medical care for vanishing twin syndrome is cord occlusion for selective termination of the weaker twin. In the case of a monochorionic twin pregnancy with an impending vanishing twin, the umbilical cord of the affected twin is surgically closed off. This deprives the nutrition and circulation and completely cuts off the weaker twin from the placental circuit but on the other hand, safeguards the other twin from an interruption in blood supply or metabolic complications.

What Happens to the Other Baby?

A vanishing twin detected early in the pregnancy rarely affects the other twin. However, if it is detected in later pregnancy, the surviving foetus has a higher risk of intrauterine growth restriction. Preterm labour might be a risk for the mother, besides abnormal bleeding and maternal infections. A few studies on vanishing twin syndrome have reported that the surviving twin might also have a higher risk of cerebral palsy after birth.

How to Prevent Vanishing Twin Syndrome

Since the main cause of the syndrome is genetic or chromosomal anomalies, there is no specific prevention for vanishing twin syndrome. Chromosomal studies and genetic workup may be advised in cases with recurrence or similar family history. Repeated, unexplained miscarriages may indicate a need for genetic counselling for the couple.

Vanishing twin syndrome is an unfortunate and unavoidable complication of multiple pregnancies. Timely diagnosis and appropriate medical care can ensure safety and well-being of the mother and the surviving twin.