Progesterone Prevents Preterm Birth for Some Women

Studies found hormone helped those with short cervix, but not those carrying twins or triplets.

By Serena Gordon
HealthDay Reporter
Wednesday, August 1, 2007; 12:00 AM

Copyright © 2007 ScoutNews, LLC. All rights reserved.

WEDNESDAY, Aug. 1 (HealthDay News) -- The hormone progesterone may help prevent preterm birth in some women, but it doesn't work for everyone.

A pair of studies in the Aug. 2 issue of the New England Journal of Medicine found that progesterone didn't help prevent preterm birth for women carrying twins or triplets, but it was helpful in women carrying a single baby who also had a condition known as short cervix.

"The phenomenon of preterm birth is complex and there are probably multiple pathways involved so, ultimately, we will probably have to have multiple solutions," said Dr. John Thorp, a co-author on the twin study and a professor of obstetrics and gynecology at the University of North Carolina at Chapel Hill.

Preterm birth is defined as birth that occurs before the 37th week of pregnancy. About 12 percent -- or one in eight -- of babies born in the United States are born preterm, according to the March of Dimes. The earlier a baby is born, the more likely it is that the baby will have health or developmental problems.

In the first study, researchers randomly assigned 661 women who were pregnant with twins to receive weekly injections of 17 alpha-hydroxyprogesterone caproate (17P) or a placebo injection. The injections began at 16 to 20 weeks of gestation and ended at 35 weeks.

The researchers found that 17P was not effective in preventing preterm birth. Delivery or fetal death before 35 weeks' gestation occurred in 41.5 percent of the pregnancies in the 17P group and in 37.3 percent of the pregnancies receiving placebo. Serious adverse events to the baby occurred in 20 percent of the 17P group and 18 percent of the placebo group, according to the study.

"This therapy that we hoped would be a magic bullet in the prevention of preterm birth was not effective for twins," Thorp said.

In the second study, researchers compared the use of vaginal progesterone to a placebo in women with a short cervix. A short cervix develops sometime during early to mid-pregnancy, according to Dr. Robert Welch, chairman and program director of obstetrics and gynecology at St. John's Providence Hospital in Southfield, Mich. Experts aren't sure exactly what causes a woman to develop a short cervix, but it's not something that can be predicted ahead of time, he noted.