Vanishing Twin Syndrome: Causes, Symptoms, and Effects

One particular risk for multiple pregnancies is vanishing twin syndrome (VTS), which causes you to lose one of your twins. It can be heartbreaking, and may leave you wondering what’s in store for the surviving twin.

Read on to learn more about VTS, including its causes, symptoms, and the potential consequences for you and your baby.

Vanishing twin syndrome (VTS), also known as disappearing twin syndrome or twin resorption, is a form of miscarriage that affects pregnancies with multiple babies. It results in the loss of one baby, but not all.

Despite the name, this syndrome can also occur if you’re carrying triplets or more.

It usually happens during the first trimester (within the first 12 weeks). You may not have any other noticeable symptoms. 1

Your sonographer (ultrasound technician) or doctor may detect VTS with an ultrasound. They may notice two or more gestational sacs or fetuses during early scans, but later scans will show fewer babies remaining, meaning at least one has “vanished.”

What happens to the lost twin?

During VTS, a twin stops developing and, in most cases, is eventually reabsorbed by the mother’s body or the placenta. It may also be absorbed by the surviving twin.

Sometimes, VTS can also result in a rare condition known as fetus papyraceous. This is where the lost twin passes away, usually early on in the second trimester, and becomes soft and mummified or flattened between the surviving twin and the uterine wall. 2 3

After you give birth, your doctor may be able to identify the compressed co-twin or remaining fetal tissue in the placenta. 4

Figuring out how often VTS happens is challenging since it normally occurs very early in pregnancy, which means it often goes undetected. However, studies estimate that VTS affects around: 4

• 36% of twin pregnancies
• 50% of pregnancies with three or more embryos

• 20%–30% of pregnancies achieved through assisted reproductive technology (ART), such as in vitro fertilization (IVF)

You’re also at a higher risk of VTS after the first trimester if your twins share a placenta. VTS is estimated to have a prevalence of above 15%–35% in these pregnancies. 5

It isn’t clear exactly what causes VTS, but several factors might affect your risk of it. 4

Genetic factors may play a big role, with the lost twin often having chromosomal abnormalities that affect his ability to thrive. 6

As a mom-to-be, your own physical condition may also affect your odds of experiencing VTS. Being older than 35 increases your risk of having multiple babies and experiencing pregnancy loss. If you have any placental abnormalities (such as it being too small), that could also play a role.

Moreover, as mentioned, the odds of VTS rise when you pursue IVF or other ART procedures, which increases your likelihood of conceiving multiple babies.

VTS doesn’t always come with symptoms at all. However, some women may experience symptoms that are similar to the signs of a miscarriage, such as: 4

• Vaginal bleeding or spotting
• Mild cramping
• Pain in the pelvis or back

Note that while these symptoms often indicate a miscarriage, they can also be common early pregnancy symptoms. 7 Talk to your doctor for a proper diagnosis.

It’s possible your doctor will also notice that you had VTS in the course of doing their usual prenatal tests, such as when they check your levels of the hormone human chorionic gonadotropin (hCG). If your weekly hCG levels were initially high enough to support twins but then leveled off, that can be a suggestive sign.

Usually, VTS in the first trimester won’t affect you or the surviving twin. 8 Moreover, if the surviving twin reabsorbs the dead fetus, it’s generally harmless. 9

However, after those first twelve weeks, VTS can cause issues.

Potential complications from vanishing twin syndrome

Later on in your pregnancy, VTS can have a bigger impact on your placenta and the flow of blood and nutrients to your surviving baby. This could result in premature birth, low birth weight, or even cerebral palsy. 10

If VTS occurs later in the pregnancy, your doctor will closely monitor you and your surviving twin for any signs of complications.

How vanishing twin syndrome affects future pregnancy screenings

If you’re undergoing (or plan to undergo) non-invasive prenatal screening (NIPS), having had vanishing twin syndrome may affect the results. This test checks the DNA from your baby, which is present in your blood. Lingering DNA from your lost baby may remain in your system for a while.

This might cause discrepancies when it comes to determining the sex of your surviving twin, as well as your baby’s risk of developing certain health conditions. 11 For accurate results, you might need to wait for about eight weeks after the loss before undergoing NIPT. 12

Usually, doctors spot vanishing twin syndrome during routine ultrasounds. Again, one common scenario is that an early ultrasound reveals multiple babies, but a follow-up check shows fewer.

You may have your first ultrasound when you’re around 12 weeks pregnant and then another between 18 weeks and 21 weeks. If you had VTS, you may learn about it around that time. 13

It’s also possible to find out you had VTS after giving birth. Your doctor may examine the placenta to look for signs of it, such as lingering fetal tissue. 4

It’s normal to experience a (rather complex) sense of loss after VTS—after all, you’re grieving one baby while still carrying another. It’s also normal to feel anxious about the health of your surviving twin. At this point, your self-care becomes paramount.

Looking after your mental health

Don’t brush off how you’re feeling, and consider talking to someone you trust. That could mean your partner, a close friend, a family member, or a therapist, but regardless, sharing your feelings will aid in your grieving process. You could also join an online or in-person support group for pregnancy loss.

As part of your self-care, eat a healthy pregnancy diet, exercise regularly, get enough sleep, and engage in activities you enjoy. Above all, while you process your loss, remember to celebrate the surviving twin.