Vanishing Twin Syndrome Overview

Pregnant couple having sonogram
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Vanishing twin syndrome is a term used to describe the spontaneous loss, or miscarriage, of one developing baby early in a multiple 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.

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.

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% of pregnancies with two gestations
  • 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 very early cases of vanishing twin syndrome (prior to an early ultrasound), the woman might never know that the condition occurred.

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.

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.

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

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.

What It Means for the Pregnancy

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. 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:

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, a fetus papyraceous remains. A fetus papyraceous is a paper-thin remnant of the baby. Uncommonly, a teratoma tumor may occur in which there are some remnants of fetal tissue, such as hair or teeth.

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 you are still pregnant with your other baby. 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.

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  1. Evron E, Sheiner E, Friger M, Sergienko R, Harlev A. Vanishing twin syndrome: Is it associated with adverse perinatal outcome?. Fertil Steril. 2015;103(5):1209-14. doi:10.1016/j.fertnstert.2015.02.009

  2. Timur H, Aksoy RT, Tokmak A, et al. Maternal and perinatal outcomes of dichorionic diamniotic twin pregnancies diagnosed with vanishing twin syndrome: A retrospective analysis from a single clinical center. Ginekol Pol. 2018;89(1):30-34. doi:10.5603/GP.a2018.0006

  3. Davies MJ, Rumbold AR, Whitrow MJ, et al. Spontaneous loss of a co-twin and the risk of birth defects after assisted conception. J Dev Orig Health Dis. 2016;7(6):678-684. doi:10.1017/S2040174416000301

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