Preterm Labor Risk Resistant to Treatment in Women With Prior History

Martha Kerr

May 12, 2008

May 12, 2008 (New Orleans) — Women with a history of preterm delivery remain at high risk despite prophylactic tocolytic therapy with 17-alpha-hydroxyprogesterone caproate (17OHPC) treatment.

Yet, this group had the greatest response to the drug among a larger group of women at high risk for preterm labor, including those with a shortened cervix, cerclage, smoking status, black race, or those who were socioeconomically disadvantaged — all known risk factors for premature labor.

Results of the well-attended and much-discussed study were presented here by coinvestigator Niki Istwan, BSN, from the Department of Clinical Research at Matria Healthcare in Marietta, Georgia, at the American College of Obstetricians and Gynecologists 56th Annual Clinical Meeting.

The study involved 1177 women at fewer than 27 weeks' gestation with singleton pregnancies and a history of preterm delivery. Women received weekly 17OHPC injections until reaching full term. Despite treatment, 246 women developed preterm labor followed by delivery and were excluded from the study.

During observation, 270 went into preterm labor and were hospitalized. Those who did not go into early labor (n = 660) were managed at home until they had a full-term delivery.

Overall, 517 women (43.9%) in the entire cohort of 1117 women receiving 17OHPC developed preterm labor, and of these, 270 (22.9%) went into labor at fewer than 34 weeks. Nearly three quarters of the women (73.3%) developing preterm labor had recurrent episodes.

"In this group of women at high risk for recurrent preterm delivery, those women receiving [17OHPC] remained at increased risk for preterm labor and preterm birth," Ms. Istwan reported.

"The only risk factor that we could identify for who might respond to 17OHPC prophylaxis was women with a previous history," she said in an interview with Medscape Ob/Gyn & Women's Health. "None of the other standard risk factors appears to influence response to treatment."

Ms. Istwan acknowledges that little is known about the tocolytic properties of 17OHPC, but she stressed that the arsenal of treatment options to prevent preterm delivery is limited. Her presentation sparked a lively discussion and much speculation.

In a separate study designed to measure uterine activity after administration of 17OHPC, Kenneth R. Barton, MD, professor emeritus of the University of Louisville, Kentucky, showed that administration of 17OHPC injections did not appear to induce a reduction in uterine contractions, as expected, among 388 women in spontaneous preterm labor.

The hormone "did not appear to exhibit tocolytic properties in women having preterm labor symptoms," Dr. Barton told Medscape Ob/Gyn & Women's Health, "even though uterine contraction increased once therapy has ended.

"We think this shows that 17OHPC has an anatomic rather than a physiologic effect on relaxing the uterus, but what this means, we don't know," he said.

Neither study received commercial grant support. Ms. Istwan and Dr. Barton have disclosed no relevant financial relationships.

American College of Obstetricians and Gynecologists 56th Annual Clinical Meeting: Posters 88 and 92. Presented May 6, 2008.

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