News Author: Anthony J. Brown, MD

April 28, 2006 — Sexual intercourse during early pregnancy does not significantly affect the risk of a recurrence of preterm birth for women with a prior spontaneous preterm delivery, new research shows. However, possibly due to infectious mechanisms, an increasing number of lifetime sexual partners do raise the risk.

Decreased physical activity, including sexual intercourse, during pregnancy is often recommended to prevent or treat preterm labor symptoms, note the authors of the study in the April issue of Obstetrics and Gynecology. Women with a prior spontaneous birth are known to be at increased risk for recurrent preterm birth and, therefore, could be prime targets for such advice.

Still, data are lacking on the effect of sexual intercourse, particularly past behavior, on the risk of recurrent preterm delivery.

In the present study, Dr. Nicole P. Yost, from Emory University School of Medicine in Atlanta, and colleagues looked at the effect of coitus on the risk of preterm birth in 187 women with singleton pregnancies who had a previous preterm birth.

The subjects' sexual history was obtained at 16 to 18 weeks of gestation by a research nurse. Data from 165 of the women were available for analysis.

Thirty-six percent of women had a spontaneous preterm birth at less than 37 weeks of gestation, the report indicates.

The number of sexual partners during the current pregnancy had no bearing on the risk of recurrent preterm birth, whereas the number of lifetime partners did. Regarding the latter finding, the rate of recurrent preterm birth ranged from 19% for women with one lifetime partner to 44% for those with at least four partners (p = 0.007).

The incidence of recurrent preterm birth among women reporting some sexual intercourse during pregnancy was 38% — higher, but not significantly different from the 28% rate seen in women who reported little or no intercourse during pregnancy.

Dr. Jeanne Sheffield, an obstetrician-gynecologist not affiliated with the present study, told Reuters Health that although many clinicians recommend against sexual intercourse during pregnancy, "every large study that has looked at coitus and preterm labor has not found an association."

As to how the number of lifetime sexual partners may impact the risk of preterm birth, Dr. Sheffield, a professor at UT Southwestern Medical Center at Dallas, said it may relate to infectious mechanisms. "The greater the number of lifetime sexual partners, the greater the risk of introducing abnormal bacteria that could potentially promote preterm labor."

The message from the present study is that sexual intercourse during pregnancy is probably okay for women who have a history of preterm birth, Dr. Sheffield said. "A possible exception is the small group of women who have a cerclage in place, ruptured membranes, or are already dilated and still preterm. For these women, we often recommend decreasing or abstaining from sexual intercourse."