Dr. Charles J. Lockwood, director of obstetrics and gynecology at Yale University School of Medicine, said, ”This is really the first innovation that’s clearly been shown to prevent or reduce the incidence of premature delivery.”
Low birth weight and serious, sometimes-deadly complications also occurred less often in babies whose mothers got the weekly progesterone injections, the researchers found.
The study, from the New England Journal of Medicine, involved women at very high risk of premature delivery, all of whom previously had at least one premature baby. Full term is considered 37 weeks to 40 weeks, and these women’s previous pregnancies averaged 31 weeks. Some of the women in the study received progesterone; a comparison group got a placebo.
The progesterone proved so effective that the study was halted early because it would have been unethical to withhold the treatment from those in the control group, researchers said.
“This is a start at finally having some successful treatments to prevent the biggest problem we have in caring for pregnant women,” said lead researcher Dr. Paul J. Meis, professor of obstetrics and gynecology at Wake Forest University School of Medicine. “We have tried so many treatments to prevent premature birth, and they have not been successful.”
Compounds of progesterone, a natural hormone that helps maintain pregnancy, were used in the 1960s and ’70s to prevent premature birth. But Meis said they fell out of favor because the few, small tests of its effectiveness had mixed results.
The study, conducted at a network of 19 clinical centers run by the National Institute of Child Health and Human Development, followed 459 women, mostly in their 20s, who had high-risk pregnancies from 1999 to 2002.
Among the women in the study who received progesterone, about 36 percent gave birth before 37 weeks, compared with 55 percent of women in the control group. About 11 percent of mothers who had progesterone shots delivered before 32 weeks, compared with about 20 percent in the other group.
The babies of mothers given progesterone also fared better, with only 27 percent weighing less than 5.5 pounds at birth, compared with 41 percent in the comparison group.
Lockwood said many doctors are starting to recommend progesterone to women with high-risk pregnancies after results of this study were reported at a February conference and because a similar study in Brazil published in February found daily vaginal suppositories of progesterone cut premature births by half.
In 2001, 11.9 percent of American babies were born before 37 weeks’ gestation, a 27 percent increase over 1981. That jump was partly fueled by more multiple births, according to the National Center for Health Statistics.
Premature birth is the country’s second-leading cause of infant mortality.