All About Vanishing Twin Syndrome

Vanishing twin syndrome (VTS) is a miscarriage that happens in pregnancies with twins. It is a condition that occurs during pregnancy when one of the twins or multiple foetuses dies in the womb and is absorbed by the mother’s body, leaving only one surviving foetus. The ultrasound stops detecting the second foetus, and it seems as if it has vanished. This typically happens early in the pregnancy, often before the mother is even aware she is pregnant with multiples. Take a look at the article to learn about this syndrome in detail.

What Happens When One Twin Absorbs Another?

During pregnancy, one twin can be absorbed by the other, the placenta, or the mother. It can happen in the form of miscarriage or vaginal bleeding/spotting without the mother's knowledge. The phenomenon can range from the disappearance of an early gestational sac to a foetus with documented heart activity.

The vanishing twin may have the following physiologic outcomes:

• Resorption

Although resorption is considered the most likely physiological explanation for the disappearance of a certain proportion of the gestational sac, the actual incidence of resorption is still unknown. Studies have shown that resorption can occur anywhere from the seventh to the twelfth week of gestation. It is evident, however, that the resorption of a gestational sac during pregnancy does not affect the co-twin. Moreover, despite the loss of one twin due to resorption, the chances of survival for the other remain high, as this phenomenon mostly occurs in the first trimester.

• Blighted Ovum

A blighted ovum is a condition where an ultrasound scan shows a gestational sac without an embryo. Studies suggest that most pregnancies that end in the disappearance of the foetus are a combination of a normal pregnancy and an anembryonic pregnancy. If you experience vaginal bleeding in the first trimester, this may indicate the expulsion of the anembryonic sac. It is important to have a thorough ultrasound examination before considering dilation and curettage, as this procedure may accidentally lead to the termination of the surviving twin.

• Foetus papyraceous

Foetus papyraceous is a rare condition where a foetus becomes mummified, compressed, or flattened due to being positioned between the membranes of a viable foetus and the uterine wall. This typically occurs in pregnancies where the mother carries twins or more babies. The deceased twin usually passes away in the early second trimester. While in some cases, complete resorption may occur, in others, the twin may become macerated, which can potentially affect the other viable twin as the pregnancy progresses. Regular ultrasonographic examinations can help monitor this process. Additionally, a vanishing twin has been linked to some foetal malformations in the surviving twin, although the mechanism behind this is not yet known.

How Common Is It?

It is now more common to diagnose vanishing twin syndrome since the use of ultrasonography and transvaginal sonography in early pregnancy. This syndrome occurs in an estimated 36% of twin pregnancies and in half of the pregnancies that begin with three or more gestational sacs. When using assisted reproductive techniques (ART), it is estimated to occur in 20-30% of pregnancies. This phenomenon is more prevalent with the use of assisted reproductive methods, as more than one embryo is transferred to the uterus, and the rate of multiple gestations increases.

Symptoms of a Vanishing Twin Syndrome

The symptoms of a vanishing twin syndrome are similar to that of a miscarriage that takes place in the first trimester of pregnancy. The common symptoms of vanishing twin syndrome are as follows:

• Uterine cramps

• Light bleeding

• Spotting

• Pelvic pain

• Back pain

What Causes Vanishing Twin Syndrome?

The most common cause of vanishing twin syndrome is chromosomal abnormalities. However, there are some other causes also. Some other causes of vanishing twin syndrome are as follows:

• Maternal age above 35 years

• The conception was through assisted reproduction technology like IVF

• Abnormalities of the placenta

• Rubella infection during pregnancy

• Genetic factors

• Irregularity in the DNA of the vanishing twin

How is it Diagnosed?

During a pregnancy ultrasound, your doctor may be able to diagnose vanishing twin syndrome if one of the earlier visible embryos is no longer present. Your doctor may also assess your human chorionic gonadotropin (hCG) hormone levels, which indicates how your pregnancy is progressing. Your body produces hCG during pregnancy, and a plateaued hCG level that was once high enough to support multiples can be a sign of vanishing twin syndrome.

Vanishing twin syndrome can be accurately diagnosed using ultrasound technology. While human error can occur during the diagnosis of VTS, it is an unlikely occurrence. It's important to note that not all cases of vanishing twin syndrome can be detected. It is possible to be pregnant with multiple embryos and miscarry one or more before your first ultrasound, which means that neither you nor your healthcare provider will know that you were initially carrying twins or triplets.

In some cases, foetal tissue from a vanished twin may be found in the placenta after delivery, which used to be the only way to detect a VTS pregnancy before ultrasound technology.