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.
For most normal pregnancies, however, if a woman feels like having sex late in pregnancy there is probably no medical reason to keep her from doing so, based on the study. But there is no medical benefit either.
Schaffir says doctors and other pregnancy caregivers should talk with their patients about sex during pregnancy.
“This discussion should not lead patients to believe that sexual intercourse will initiate labor sooner,” he wrote. “Patients may continue to hear from relatives and other ‘old wives’ that intercourse will hasten labor, but it should not be given credence by the medical community.”
Hope Ricciotti, MD, an ob-gyn at Beth Israel Deaconess Medical Center, says she is surprised by the findings.
“This is one that many of us believed because of the hormonal involvement,” she tells WebMD.
Other Things to Try
Another method to hasten delivery that doctors often suggest to women is nipple stimulation, since it promotes the production of another hormone involved in labor induction known as oxytocin.
Nipple stimulation does cause contractions while the woman is doing it, Ricciotti says. But once the woman stops, so do the contractions. Ricciotti knows of no case where a woman actually put herself into labor using this method.
Other doctors perform a vigorous pelvic exam when the cervix is slightly dilated in an effort to get things moving. While there is some evidence this is effective, it is not conclusive, Ricciotti says.
Otherwise, you can always try food. Although there is no medical evidence to back it up, countless women are convinced eating pizza or Chinese food put them into labor.
“The big one is Chinese food,” Ricciotti says. “Eggplant was in vogue for a few years, but there was no evidence at all that it worked.”