As we celebrate the annual Twins Days festival in Twinsburg, Ohio, this weekend, it's a good time to talk about the declining rates of twins in the U.S.
Why it matters: After a major national twin birth boom or "twinflux," twinning rates (an actual science term) have been dropping.
What's happening: In vitro fertilization — which gained popularity after the first IVF baby was born in 1978 — contributed to an increase in twin births.
- Doctors used to transfer multiple embryos into the uterus of a patient trying to conceive, with the hopes of at least one leading to pregnancy.
- The increase in average maternal age was also a factor, since the likelihood of spontaneously conceiving twins increases with age.
Yes, but: After advances were made in IVF in the early '00s, implantation rates improved and some experts started to discourage multiple embryo transfers.
- The thinking: Transferring only one embryo would avoid twin pregnancies, which remained risky.
As of 2020, more than 80% of U.S. embryo transfer cycles involve only a single embryo, according to CDC data. And in the last few years, there's been a dip in twin birth rates.