Vanishing Twin Syndrome Statistics

Research Suggests that Around a Third of Twins Are Lost Early In Pregnancy

Pregnant couple having sonogram
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Vanishing twin syndrome is a term for the spontaneous loss, or miscarriage, of one developing baby early in a multiple pregnancy

An expectant mother might have an early ultrasound that detects two gestational sacs. But later on, only one fetal heartbeat is detectable and the second sac has disappeared. Or one normally developing baby is present alongside a blighted ovum.

Some texts use the term "vanishing twin" 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.

What Are the Vanishing Twin Syndrome Statistics?

The vanishing twin phenomenon appears to be common. Research suggests that vanishing twin syndrome occurs before the 12th week of pregnancy in:

  • around 36 percent of pregnancies with two gestations
  • more than 50 percent of pregnancies 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 percent of twin gestations and 4.3 percent of triplet gestations will be affected by fetal death, although these are generally not considered vanishing twin pregnancies.

Are There Symptoms?

In very early cases of vanishing twin syndrome, the woman might never know that the condition occurred.

In other cases, the loss of the twin might be accompanied by some miscarriage symptoms such as vaginal bleeding and hCG levels that rise more slowly than in normally developing twin pregnancies.

What Causes It?

If you lost one of your pregnancies 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 researchers do not fully understand why one twin is lost in other cases of vanishing twin syndrome.

What It Means for the Surviving Baby

Although there is some debate around this, there's growing evidence that there may be a greater risk of certain pregnancy problems after a twin "vanishes." An Australian study of pregnancies conceived by in vitro fertilization published in 2011 found more congenital defects (such as cerebral palsy) in babies who had a vanishing twin, compared to babies that were conceived without a twin. And in 2015, Israeli researchers found a higher risk of several adverse outcomes to the mother and surviving twin in vanishing twin pregnancies:

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. 

Coping with Vanishing Twin Syndrome

If you have been diagnosed with vanishing twin, you probably have a lot of mixed emotions. It's normal to grieve the baby you lost while also feeling relief that you are still pregnant with the viable baby. You should not feel that you have to pick and choose between your emotions. No rules say you cannot be sad and happy at the same time, and you shouldn't feel that you are dishonoring either baby if you go through a normal grieving process while continuing to eagerly anticipate your viable baby.

Sources:

Twin pregnancy: Prenatal issues. UpToDate. January 12, 2016.

Evron, E., Sheiner, E., Friger, M., et al. (2015). Vanishing twin syndrome: is it associated with adverse perinatal outcome? Fertility and Sterility.

'Vanishing twin' explains increased risk of birth defects. ScienceDaily. July 5, 2011.

Landy, H.J. and Keith, L.G. (1998). The vanishing twin: a review. Human Reprouction Update.

Johnson, C.D. and Zhang, J. (2002). Survival of Other Fetuses After a Fetal Death in Twin or Triplet Pregnancies. Obstetrics & Gynecology.

Kelly, M.P., Molo, M.W.. Maclin, V.M., et al. (1991). Human chorionic gonadotropin rise in normal and vanishing twin pregnancies. Fertility and Sterility.

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