Getting an early ultrasound has many benefits, in part because the sooner you and your doctor discover that you have more than one baby to care for, the better care you and your babies will be able to receive.
Identifying twin pregnancies earlier than ever also can reveal losses that would have gone undetected before the days of first trimester ultrasounds. When the miscarriage of a twin (or a triplet) occurs, the phenomenon is known as vanishing twin syndrome.
What is vanishing twin syndrome?
Vanishing twin syndrome is the loss of one twin during pregnancy, usually in the first trimester, and oftentimes before the mother even knows she's carrying twins. When this happens, the tissue of the miscarried twin is usually reabsorbed by the mother's body over time.
In the (rarer) case of a twin dying in the second or third trimester, the loss isn't usually referred to as vanishing twin syndrome, but rather, 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 percent 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]
Documented rates of vanishing twin syndrome have grown significantly over the past few decades, as early ultrasounds — the only way to be sure that you're carrying twins early in pregnancy — have become more routine.
Vanishing twin syndrome symptoms
Oftentimes, 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]
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 miscarried a twin, or you may find out on your first ultrasound that there is a second gestational sac that does not contain a living twin. The only sign of vanishing twin syndrome may be a later ultrasound that shows that there are no longer two fetuses in the womb.
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Even if you have symptoms that are similar to those of a miscarriage, none are a sure 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 have 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. However, that might be because older mothers, in general, have higher rates of multiple pregnancies.[3]
Is vanishing twin syndrome hereditary?
It's not known whether vanishing twin syndrome is hereditary, in part because doctors aren't exactly sure what causes the phenomenon. Plus, early ultrasounds are still relatively new, so 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, when vanishing twin syndrome occurs in the first trimester, the mother goes on to experience a normal pregnancy and delivers the single healthy baby without complication or intervention. Some research done in people who used IVF to get pregnant shows that women who've experienced vanishing twin syndrome can be more likely to give birth to a premature baby or a baby with low birth weight compared to women who didn't have vanishing twin syndrome.
If you have had a vanishing twin in the first trimester, some genetic screening test results may not be as accurate for the remainder of your pregnancy. It will be important to discuss any screenings with your doctor in this case.
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 this case, your practitioner will carefully monitor the health and growth of your remaining twin and watch you closely for signs of complications.
If you've experienced the first trimester loss of a twin (or if your loss occurred later in pregnancy), you may feel a combination of grief over the demise of one baby and relief for the viability of the surviving baby. Allow yourself (and your partner, if you have one) to grieve. Remember to acknowledge the loss of your child and the loss of your identity as parents of multiples, and to also celebrate the life of your surviving baby.
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