Why does sperm help induce labor

NEW YORK - Despite a widespread belief that sex during the later stages of pregnancy can jumpstart labor, a new study from Malaysia found no differences in the timing of delivery between women who had sex near term and those who abstained. Tan Peng Chiong, an obstetrics and gynecology professor at the University of Malaya, and one of the authors of the study. Tan said that many women believe intercourse can induce labor, and scientists have proposed plausible biological explanations for why it might help.

For one, semen contains a hormonelike substance called prostaglandin, which is used in synthetic form to induce labor. Breast stimulation is also thought to hasten labor and orgasm can trigger uterine contractions. Tan said the belief also probably came from "the deep seated folk perception that intercourse in pregnancy may be unsafe and may cause pregnancy expulsion or miscarriage despite fairly replete evidence to the contrary. But few studies have ever investigated whether sex really can initiate labor, and the small amount of existing evidence was inconclusive, Tan and his colleagues write in the obstetrics and gynecology journal BJOG.

So they set out to see whether advising women to have sex during the final weeks of pregnancy could help them avoid an induction. The researchers invited more than 1, women to participate, all of whom were 35 to 38 weeks pregnant the typical pregnancy lasts 40 weeks and none of whom had had sex in the previous six weeks.

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It's long been used as a natural method to try to induce labor. But is there solid scientific evidence that sex brings on labor? Human semen contains substances called prostaglandins, which are hormone-like substances that can help ripen the cervix and therefore help labor begin.

Additional prostaglandins are released by the woman during sex. Because synthetic prostaglandins are used as a method of cervical ripening for labor induction, it seems logical that natural sources might also be useful.

Pitocin is a synthetic form of oxytocin that is used to cause uterine contractions and speed up labor , so this natural way to release it also would seem to be a logical way to stimulate labor. Female orgasm creates uterine contractions as well. All of these factors might promote cervical ripening and hasten labor. This is an area that has little high-quality research, but there have been some newer studies performed. Perhaps the better method for giving a reliable answer is a randomized controlled trial where one group of women have vaginal intercourse at least twice a week late in pregnancy and a similar group abstains from sex.

A study of this design enlisted women who had a low-risk singleton term pregnancy. It found that vaginal intercourse did not hasten spontaneous labor onset at term. A study from Malaysia enlisted over women, with half advised that coitus late in pregnancy after 35 weeks of gestation could be used as a natural method to safely expedite labor.

They were to keep a coitus diary and those who didn't return it were contacted for a phone interview. The women who were told that coitus could hasten labor had more sex than the control group. However, there was no difference between the two groups of women in labor onset and the need for artificial labor induction.

Another study by the Malaysian researchers found that women who reported coitus were actually less likely to go into spontaneous labor before their scheduled labor induction. But they were happy to report that there was no association with adverse pregnancy outcomes for coitus and orgasm. An Iranian study of sex in the last week of pregnancy concluded it might be associated with the onset of labor. All of these studies and older studies found there were no harmful effects of having sex late in pregnancy for low-risk pregnancies.

There are many reasons why very pregnant women might not want to have sex.