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Late-Pregnancy Sex Doesn't Speed Labor

June 2, 2006 - The notion that having sex late in pregnancy will hasten labor and delivery is among the oldest of old wives' tales. But it looks like the old wives were wrong.

Women with a low risk of complications who had sex in the final weeks of pregnancy actually carried their babies slightly longer than those who abstained from sex during that time, according to a new study reported in the June issue of Obstetrics and Gynecology.

And the full-term babies born to women who had late-pregnancy sex were just as healthy as those born to women who did not.

"This study should reassure low-risk women that there is probably no harm in engaging in intercourse late in pregnancy," says obstetrician Jonathan Schaffir, MD, of the Ohio State University Medical Center. "But it showed no particular benefit, either, in terms of inducing labor."

Sex Wasn't a Factor

There is actually sound medical reasoning for the idea that sex might bring on labor. Male semen contains hormone-like chemicals known as prostaglandins. Prostaglandins can be used for cervical ripening, in which the cervix physically changes in preparation for labor. Also, female orgasm can bring on uterine contractions.

But there is little clinical evidence that intercourse influences the outcome of normal pregnancies. The study cites one analysis of 59 studies that found no association between sex and preterm birth, premature amniotic sac rupture, or low birth weight in low-risk pregnancies.

Schaffir's study included 93 low-risk pregnant women past the 37th week of their pregnancy. (At 37 weeks a pregnancy is considered full term.) The women were asked during weekly doctor's office visits about their sexual activity.

Half the women reported having sex involving penetration after that time.

Cervical examinations were performed at each weekly visit to determine if sexual activity affected cervical ripening. No correlation was seen between the frequency of sexual intercourse and cervical change.

And the sexually active women in the study actually carried their babies an average of four days longer than women who abstained from sex -- 39.9 weeks compared with 39.3 weeks. Schaffir says this small difference could be because women closer to labor simply felt less comfortable and were, therefore, less likely to engage in sex.

The lack of a difference in cervical changes, combined with the absence of a meaningful difference in delivery dates among women who had sex, suggests sexual intercourse had no effect on inducing labor, the researchers concluded.

High-Risk Women Should Abstain

The findings do not suggest all women can safely engage in sex late in pregnancy. Women with risk factors for preterm delivery should probably avoid sex and should definitely discuss the issue with their health care provider. Risk factors for preterm delivery include having had a previous preterm birth, having uterine bleeding during pregnancy, contracting certain vaginal infections, and having other pregnancy-related complications.