The most dramatic shift in twin birth rates occurred in older moms. For moms age 35 – 39, twin rates increased 100%, and for moms over 40, twin rates increased 200%.
The older you are, the more likely you are to have twins, but researchers think that most of this shift can be attributed to fertility treatments. One-third of the twins born to older moms are likely due to maternal age, and two-thirds are due to fertility therapies such as drugs or in-vitro fertilization.
The rates of twins born to mothers under 20, age 20 – 24, and age 25 – 29 have also increased, from 12.8 to 16.3, 17.4 to 23.3, and 20.5 to 30.6 twins per 1,000 births, respectively. While some of these younger women do undergo fertility treatments, researchers say the more significant factor may be birth control pills. “Your chance of conception of twins is also higher right after you get off the birth control pill. So that may be why we’re seeing it among younger women, since there is more widespread use of birth control pills,” says Barbara Luke, a professor of obstetrics, gynecology, and reproductive biology at Michigan State University.
Interestingly enough, twin rates from 2005 – 2009 slowed a bit, as fertility specialists are making extra efforts to reduce the multiple birth rate.
Source: USA Today
Image: Reto Stauffer