August 1, 2007

BIRMINGHAM, Ala. -- Progesterone therapy does not reduce the chances of preterm birth in women pregnant with twins, even though earlier studies demonstrated it reduces the chances of preterm birth in women carrying a single baby who had delivered a singleton prematurely in the past, according to University of Alabama at Birmingham (UAB) researchers. The study is published in the Aug. 2 edition of the New England Journal of Medicine.

"Our study shows that progesterone therapy is not appropriate for all women at risk for giving birth prematurely," said lead author Dwight J. Rouse, M.D., professor of obstetrics and gynecology at the UAB School of Medicine, who performed the study with colleagues from the National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units Network

Rouse's team of researchers looked at 655 women pregnant with twins. The women were randomly assigned to receive weekly injections of a placebo or the form of progesterone known as 17-alpha hydroxyprogesterone caproate (17P). Progesterone is a female hormone produced in large quantities during pregnancy. It was reported in 2003 that weekly injections of progesterone reduced the risk of preterm birth by 34 percent among women who had given birth prematurely in an earlier pregnancy.

The injections started when the women were 16-20 weeks pregnant and continued until the 35th week of pregnancy or until the woman gave birth. Women in both groups had similar characteristics, including age, race and marital status. Whether the child was conceived using assisted reproductive methods or conceived spontaneously did not affect the results, nor did the type of placenta - one shared by the two babies or two separate placentas.

Of women pregnant with twins, 41.5 percent of women on progesterone treatments delivered prematurely, before 35 weeks, or experienced fetal loss. Fetal loss describes loss of the baby due to factors including stillbirth or miscarriage. By comparison, 37.3 percent of women receiving placebo injections delivered prematurely or experienced fetal loss.

"We found that the use of progesterone did not reduce premature birth in twin pregnancies when compared with the placebo group," Rouse said. "There was no difference in the amount of time the babies spent in the womb before they were delivered between the two groups. Also, progesterone treatment did not affect the proportion of deliveries before 37 weeks or before 32 or 28 weeks, when compared to the placebo group. So far, this evidence supports that injections of 17P therapy as a means to prevent preterm birth only in women pregnant with a single baby who are at risk for premature delivery because of a prior spontaneous preterm birth."