Vanishing twin syndrome is the spontaneous loss, or miscarriage, of one developing baby early in a multiple pregnancy, usually resulting in a normal singleton pregnancy. It may also be called disappearing twin syndrome.

An early ultrasound might detect two gestational sacs, but later on, only one fetal heartbeat is detectable and the second sac has disappeared. Or, in a subsequent ultrasound, one normally developing baby is present alongside a blighted ovum.

Sometimes the term "vanishing twin" is used for any pregnancy in which one baby in a multiple pregnancy is lost while the other survives, even if the twin has not technically vanished. However, the term is usually reserved for a twin that vanishes in the first trimester.

Statistics

Studies suggest that vanishing twin syndrome occurs before the 12th week of pregnancy in around 36% of pregnancies with two gestations, and more than 50% of pregnancies with three or more gestations.﻿﻿ Researchers suspect, however, that vanishing twin syndrome may be even more common, because it may frequently occur without detection.

In multiple pregnancies that have continued beyond 20 weeks, researchers estimate that about 2.6% of twin gestations and 4.3% of triplet gestations will be affected by fetal death. However, these are generally not considered vanishing twin pregnancies.﻿﻿

Vanishing Twin Syndrome Symptoms

In some cases, the loss of the twin may be accompanied by miscarriage symptoms, such as vaginal bleeding. If hCG levels are being measured, they may show a slower rise than would be expected in a normally developing twin pregnancy. In very early cases (if the twin vanished prior to an early ultrasound), the woman might never know that the condition occurred.

Causes

If you lost one of your babies during a multiple pregnancy, there's no reason to believe that it happened because of anything you or anyone else did or did not do. Some cases of vanishing twin syndrome occur because of chromosomal abnormalities in the lost baby, but in other cases, researchers do not fully understand why one twin is lost.﻿﻿

There appears to be a significant increase in vanishing twin syndrome in recent years. Since many vanishing twins would never be detected without early ultrasound, advances in technology could be part of the reason for the increase. In addition, fertility treatments are becoming more common and often increase the chance of multiples. This may also be a factor.

Diagnosis of Vanishing Twin Syndrome

Vanishing twin syndrome is typically diagnosed by ultrasound. If an early ultrasound shows a twin pregnancy, but a mother experiences symptoms of miscarriage or lower-than-expected hCG levels, or only one heartbeat can be detected via Doppler, a doctor may suspect vanishing twin syndrome. A follow-up ultrasound can determine if one twin has been lost.

Treatment

Generally, and especially when vanishing twin syndrome occurs in the first trimester, no treatment is necessary for the mother or the remaining fetus. If a twin dies later in pregnancy, there is a risk of preterm labor, infection, or hemorrhaging. In those cases, doctors will prescribe treatment appropriate for those conditions.

Although there is some debate around this, there's evidence that there may be a greater risk of pregnancy problems after a twin vanishes. Several studies have now looked at babies who had a vanishing twin compared to babies that were conceived without a twin or had a healthy twin.

Several outcomes have been noted, but in general, the risk of birth defects and complications appears to be higher in babies who had a vanishing twin. The increase in risks appears to be most common with the loss of a co-twin between six and eight weeks gestation.﻿﻿ Complications may include:

Gestational diabetes

A higher risk of congenital defects, such as cerebral palsy

Intrauterine growth restriction (IUGR), a condition in which the baby does not grow as well as it should during pregnancy

Very low birth weight

Low Apgar scores

Perinatal mortality (infant death)

For these reasons, your doctor might want to keep a closer eye on your pregnancy if you had a vanishing twin. However, it's important to note that in most cases of vanishing twin syndrome, the surviving baby is not adversely affected.

If the Twin Doesn't Disappear

Most often the vanishing twin is absorbed by the mother's body so that there is no evidence of the twin at the time of delivery. Sometimes, if a twin vanishes between 15 and 20 weeks gestation, a fetus papyraceous remains. This is a paper-thin remnant of the fetus. Uncommonly, a teratoma tumor, in which there are some remnants of fetal tissue, such as hair or teeth, may occur in the surviving twin (this is not dangerous to the baby).

Coping

If you have been diagnosed with vanishing twin syndrome, you probably have a lot of mixed emotions. It's normal to grieve the baby you lost while also feeling relief that your other baby survived. You should not feel that you have to pick and choose between your emotions. You are not dishonoring either baby if you go through a normal grieving process while continuing to eagerly anticipate your healthy baby.