If an early ultrasound revealed you were having twins only to find soon after there's just one baby, you've probably experienced vanishing twin syndrome. In this very early miscarriage, the tissue from the vanishing twin is reabsorbed by your body, and the remaining baby continues to develop normally.
Learn how you might find out about a vanishing twin and what happens if you have one.
What is vanishing twin syndrome?
Vanishing twin syndrome is the loss of one twin during pregnancy, usually in the first trimester and often before you even know you're carrying twins. When this happens, the tissue of the miscarried twin is usually reabsorbed by your body over time.
"At our 8-week scan there were two babies, one measuring 6 weeks with no heartbeat, and the other healthy at 8 weeks," says What to Expect Community mom bbmumm. "With every reoccurring ultrasound, the second sac got smaller and was eventually fully absorbed by my 20-week appointment."
In the rarer case of a twin dying in the second trimester or third trimester, the loss isn't usually referred to as vanishing twin syndrome, but rather as the loss of a twin or multiple.
How common is vanishing twin syndrome?
Vanishing twin syndrome is thought to occur in about 10% to 40% of multiple pregnancies, although experts say that it's difficult to pinpoint exactly how common the phenomenon is, in part because not all pregnant women receive first trimester ultrasounds.[1]
Getting an early ultrasound has many benefits. The sooner you and your doctor know you're expecting multiples, the sooner you can receive the specialized care you and your babies may need. But early ultrasounds have also significantly increased documented rates of vanishing twin syndrome in recent years, as they're the only way to be sure you're carrying twins early in pregnancy.
What are the symptoms of vanishing twin syndrome?
Often, there are no symptoms at all. However, some mothers experience symptoms similar to miscarriage, including:
- Mild cramping
- Vaginal bleeding
- Pelvic pain
- Decreasing hormone levels (hCG, as detected by blood tests) [2]
"At about 10 weeks I found out that twin B was gone. I didn't experience any symptoms, just that one ultrasound showed two babies with two heartbeats and the next there was one," says Community mom sammie_berends. "It's an emotional roller coaster."
How will you know for sure if you miscarried one twin?
If you don't have an early ultrasound, you may never know that you were carrying twins. In some cases, a first ultrasound may show a second gestational sac without a viable embryo.
"I had my first ultrasound today at 9 weeks to find we were expecting twins, but one sac was empty while the other had a fully healthy baby with a perfect heartbeat," says Community mom omwmanderzz.
Often, the only sign of vanishing twin syndrome is a later ultrasound that shows that there are no longer two fetuses.
Even if you have symptoms that are similar to those of a miscarriage, they aren't a definite sign of a pregnancy loss. If you do experience any of these symptoms or are concerned you might be experiencing vanishing twin syndrome, don't hesitate to call your doctor.
Who is most at risk for vanishing twin syndrome?
Women who conceive through in vitro fertilization — in which one or more fertilized eggs are placed in your uterus in the hopes that one of them will implant and become a pregnancy — may have a higher risk of vanishing twin syndrome than those who conceive naturally. Conceiving with IVF increases the chances that you'll become pregnant with multiples and therefore increases the chances that not all of those fetuses will be viable.
Women over 30 may also be more likely to experience vanishing twin syndrome, possibly because they have higher rates of multiple pregnancies. [3]
Is vanishing twin syndrome hereditary?
It's not known whether vanishing twin syndrome runs in families. Researchers still aren't sure what causes it, and because early ultrasounds are relatively new, there's limited long-term data. Experts haven't been able to study vanishing twin syndrome in a person's family history.
What is the impact of vanishing twin syndrome on the surviving twin?
In many cases, especially when the loss occurs in the first trimester, the pregnancy continues normally, and the remaining baby is born healthy without complications.
"It was heartbreaking," says Community mom CJ022022. "Going from one, then two, then back to one. So many emotions. On the upside, I have a healthy 1-year-old girl, and the vanishing twin didn't have any effect on her development. I think it was my biggest fear that I'd lose both."
Some research suggests that pregnancies following vanishing twin syndrome (particularly after IVF) may have a slightly higher chance of preterm birth or low birth weight.
It's also important to note that some genetic screening test results may be less accurate after a vanishing twin. Be sure to discuss screening options with your provider.
If a twin dies in the second or third trimester, the remaining baby may be at an increased risk of intrauterine growth restriction (IUGR), and the mother may be at risk of preterm labor, infection, or hemorrhaging. In these cases, your practitioner will carefully monitor the health and growth of your remaining twin and watch you closely for signs of complications.
How can I cope with vanishing twin syndrome?
If you've experienced the loss of a twin, your emotions may feel complicated. You may feel a combination of grief for the baby you lost alongside relief for the baby who's still growing.
"I'm 8 weeks and found out that our baby A didn't make it, but baby B looks healthy," says Community mom alexrose33. "It's really hard and complicated to hold all of the different emotions."
Both feelings are valid. Allow yourself space to grieve — not just the loss of your baby, but also the loss of the future you imagined as a parent of multiples — while also celebrating the life of your surviving baby.
Connect with other pregnant moms in similar circumstances, get more expert advice, and track your pregnancy in our free What to Expect app.
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