Roughly 10,000 preterm births could have been prevented in the United States in 2002 had hormone therapy been used, research shows.

Every year, many high-risk women go into labor early and deliver preterm babies. But weekly injections with a hormone derivative of progesterone reduces such deliveries by a third, the data show.

A collaborative group that includes the March of Dimes, the CDC, and the National Institute of Child Health and Human Development wants the hormonal treatment to be offered to pregnant women with a history of preterm delivery who are less than 20 weeks pregnant carrying a single child.

The group is also calling for more research to determine if other high-risk pregnant women would benefit from the treatment.

Their report is published in the February issue of the journal Obstetrics and Gynecology.

“We recognize that this treatment isn’t going to prevent all premature births, but we need to get a better idea of just who will benefit,” analysis co-author Richard H. Schwartz, MD, tells WebMD.

Preterm Deliveries Are Increasing

The rate of premature births, defined as birth before the 37th week of pregnancy, has risen by almost a third in the United States since the 1980s. One in eight babies in the U.S. are born early, totaling about 470,000 births each year.

The newly published analysis was based on a landmark study from 2003, which found that weekly injections of a derivative of the hormone progesterone led to a dramatic reduction in premature births among women with a history of premature delivery.

Two-thirds of the women in the study were treated with 17-alpha-hydroxyprogesterone caproate, better known as 17P, beginning at week 16 to 20 of pregnancy and ending at week 36. The rest of the women got placebo injections.

The finding that 17P led to a 34 percent reduction in preterm deliveries prompted the American College of Obstetricians and Gynecologists to recommend the treatment for women who had given birth prematurely and were pregnant again with a single child.

Progesterone has been found to help stabilize the endometrial lining, which relaxes the muscles of the uterus and prevents premature contractions.

But it is not clear if women who are eligible for the treatment are getting it, says Joann R. Petrini, PhD, who is the lead researcher of the newly published analysis. She is director of the March of Dime’s Perinatal Data Center.

Petrini and colleagues examined birth data from 2002 to understand better the potential impact of treating all eligible women with 17P. They estimated that 10,000 of the 30,000 premature births that occurred among the eligible women could have been prevented if they had been on 17P.

While that represents just a 2 percent decrease in the overall preterm delivery rate, Petrini tells WebMD that it is a significant first step in preventing the potentially devastating pregnancy outcome.

“A 2 percent reduction sounds small, but 10,000 births is significant,” Petrini tells WebMD. “We are very optimistic about this intervention and hope that the research will continue.”

Nancy Green, MD, who is medical director of the March of Dimes, says 17P may prove beneficial for other groups of high-risk women, such as those who are giving birth to twins or triplets or first-time moms with other risk factors. But she added that since there appear to be many causes for preterm delivery, no single treatment is likely to work for everyone.

“The question is, will 17P prevent all premature births or is it a drop in the bucket?" she tells WebMD. “It is becoming clear that the answer is somewhere in the middle. It is not a cure nor is it only a drop in the bucket.”

By Salynn Boyles, reviewed by Brunilda Nazario, MD

SOURCES: Petrini, J. Obstetrics and Gynecology, February 2005; vol 105. Joann R. Petrini, PhD, MPH, director, Perinatal Data Center, March of Dimes. Nancy Green, MD, medical director, March of Dimes. Richard H. Schwartz, MD, vice chairman of obstetrics and gynecology, Maimonides Medical Center, New York; past president, American College of Obstetrics and Gynecology. Nancy S. Green, MD. WebMD Medical News: “Hormone Prevents Pre-term Births.”