Dramatic Rise In US Twin Birthrates: Study
April 3, 2012

Dramatic Rise In US Twin Birthrates: Study

One in every 30 babies born in the United States in 2009 was a twin, a dramatic increase from the one-in-53 babies born a twin in 1980, a new study finds.

Researchers attribute the rise in twin birth rates, in part, to the growing number of women having children at older ages, and the expanding availability of fertility treatments.

"Prior to 1980, the incidence of U.S. twin births was stable at about 2 percent of all births, but it has risen dramatically in the past three decades," said Barbara Luke, a researcher at Michigan State University's College of Human Medicine's Department of Obstetrics, Gynecology and Reproductive Biology.

While the increase in twin birth rates held true for mothers of all ages, the largest increase was seen among women aged 30 and older.

"Older maternal age accounts for about one-third of the rise, and two-thirds is due to the increased use of fertility treatments,” including both assisted reproductive technologies and ovulation stimulation medications.

About 12 percent of U.S. women have undergone fertility therapies.

"With multiple births though there are greater health risks," Luke cautioned, noting that births for triplets and higher numbers also grew from one-in-2,702 babies in 1980 to one-in-651 babies in 2009.

Luke presented the findings this week at the 14th Congress of the International Society of Twin Studies in Italy, a conference that brings together experts from across the world to study multiple pregnancies and better understand the health impacts.

In other research presented at the conference, Luke reported that early embryo loss is associated with a significantly increased likelihood of lowered birth weight for the surviving fetuses.

Previous findings have shown mothers using fertility treatments experience more adverse health outcomes than spontaneous-conception pregnancies.  Luke and colleagues hypothesized that the residual effects of fetal loss may impact the subsequent growth and birth weight of the surviving fetuses.