What is vanishing twin syndrome: Causes, symptoms and diagnosis

Vanishing twin syndrome happens when an early scan reveals a twin pregnancy, but only one baby is seen at a later scan. It is the phenomenon of a twin or multiple ‘disappearing’ in the uterus during pregnancy, as a result of miscarriage. The foetal tissue is usually absorbed by the other twin, multiple, placenta or the mother. This gives the appearance of a “vanishing twin.” Let us examine this condition in detail, together with vanishing twin syndrome symptoms.

Vanishing twin syndrome symptoms and causes

In most cases, the cause of vanishing twin syndrome is unknown. 

Analysis of the placenta and/or foetal tissue has frequently revealed chromosomal abnormalities in the vanishing twin, while the surviving twin is usually healthy. Improper cord implantation may also be a cause.

Twins ultrasound

Estimates indicate that vanishing twin syndrome occurs in 21-30% of multifoetal pregnancies.

In pregnancies achieved by in vitro fertilisation (IVF), “it frequently happens that more than one amniotic sac can be seen in early pregnancy, whereas a few weeks later there is only one to be seen and the other has ‘vanished’.”

Research indicates more cases of vanishing twin syndrome in women over the age of 30. This may be due to the fact that older mothers in general have higher rates of multiple pregnancies, especially with the use of fertility treatments.

Symptoms of vanishing twin syndrome, if any, usually begin early in the first trimester, and include:

• Mild cramping
• Vaginal bleeding
• Pelvic pain
• hCG (hormone) levels that rise more slowly than in normally developing twin pregnancies (as detected by blood tests)

Often, there are no symptoms at all. Pregnant women should seek medical attention if they are experiencing bleeding, cramping, and pelvic pain. 

Diagnosing Vanishing Twin Syndrome 

In the earlier days, before ultrasound was available, the diagnosis of the death of a twin or multiple was made through an examination of the placenta after delivery. Today, ultrasounds have made it possible to diagnose vanishing twin syndrome. 

For example, a mum-to-be may have an ultrasound at 6 or 7 weeks gestation. The doctor identifies two foetuses, and she is told she is having twins. When she returns for her next visit though, it is possible that only one heartbeat can be heard, and a second ultrasound reveals the presence of only one foetus in the uterus. Then the diagnosis of vanishing twin syndrome is given.

In some cases, vanishing twin isn’t determined until the baby is delivered. Some foetal tissue from the twin that stopped growing may be visible in the placenta after delivery.

In case of IVF, there is closer monitoring, and so it is easier to detect this phenomenon. When checking and counting is done on the numbers of fertilised eggs implanted and, their subsequent growth so carefully monitored, it is easier to see when something has gone wrong.

Treatment of vanishing twin syndrome: Risk factors

If you miscarry a twin during the first trimester, neither the surviving twin nor the mother would require special medical treatment. In most cases, your pregnancy will continue as it would have if you were carrying one baby to begin with.

However, if the foetal death is in the second or third trimester, the pregnancy may be treated as high-risk, and require more testing and monitoring.  In most cases of a vanishing twin, the surviving baby is born healthy and without any congenital problems.

However, studies have shown that, if the twin dies in the second or third trimester, there are increased risks to the surviving foetus, including a higher rate of cerebral palsy. Premature labour, low birth weight, infection and bleeding are some other complications associated with a miscarriage happening in the later stage.

If the miscarriage occurs before eight weeks of gestation, the vanishing twin is absorbed by the remaining foetus, so there is no evidence of the twin at the time of delivery. Sometimes, instead, a paper-thin remnant of the twin remains, which is referred to as a foetus papyraceous.

Do remember that in cases of vanishing twin syndrome, it is normal to experience conflicting emotions like extreme sadness for the baby you lost, and relief and happiness for the baby who survived. Do share your feelings with your partner or someone you trust. Give yourself extra self-care and time to heal.

(Source: American Pregnancy, Verywellfamily, Healthline)