Q&A: What is vanishing twin syndrome? Should I be worried?

Vanishing twin syndrome occurs when one twin is lost while the other survives. Before routine use of ultrasound we didn't find out about most cases of vanishing twins because the mom never knew she was carrying twins to begin with. Now with frequent use of ultrasound and the increase in the incidence of multiple pregnancy via assisted reproductive techniques, vanishing twin seems like a common occurrence. About one in four twin pregnancies diagnosed before 7 weeks will turn out to only be a singleton at term.

After 8 weeks, a vanishing twin is not so common. One large study of twin pregnancies showed about a 5 percent loss of one of the twins after mid pregnancy. Many of these occur in high-risk pregnancies, when the twins share a sac or some part of the placental circulation. Typically twin pregnancies are monitored by frequent ultrasounds, so the growth and well-being of the babies can be assessed regularly. Once you get past about 8 weeks, the greatest likelihood is you will have two new family members to take home and love.