USA Today reports on data from the U.S. Centers for Disease Control and Prevention (CDC) showing the number of twin births in the United States more than doubled from 1980 to 2009.
The analysis of three decades of twin births finds big increases across all age groups, all racial and ethnic groups, and in all 50 states plus the District of Columbia. The overall U.S. twin birth rate increased 76%, from 18.9 per 1,000 births in 1980 to 33.2 in 2009 — roughly 1-in-30 of today’s births are twins compared to 1-in-53 in 1980.
Twin rates have “skyrocketed” for older women, USA Today’s Sharon Jayson writes, citing National Center for Health Statistics (NCHS) findings that among women 35-39, rates rose by nearly 100%, and for those 40 and over, rates increased more than 200%.
Age does factor into the likelihood of having twins, but the larger catalyst for the surge in twins is the rise in fertility treatments, according CDC statistician Joyce Martin — roughly 1/3 of the increase is attributed to older moms and 2/3 is the result of fertility-enhancing therapies such as drugs and technologies like in-vitro fertilization.
Michigan State University professor Barbara Luke added that the increase in twins among younger women is likely the result of more widespread use of the birth control pill over the past 30 years. Luke, a professor of obstetrics, gynecology and reproductive biology explained the conception of twins is higher shortly after women stop taking birth control.
Some fertility specialists are aiming to reduce the rate of twin births, which add risk and complication for both moms and babies. While most twins are delivered safely and grow up fine, twins are more likely be born earlier and smaller, tend to require more hospitalization, and they have higher infant mortality rates.