Medical myth: Sex induces labour

Sex. It's what got you into pregnancy, but is it also the pathway to getting you out?

Around a quarter of all Australian pregnancies are medically induced, with a third of those inductions occurring due to pregnancy continuing beyond term (40 weeks). Induction is not without its risks and discomfort and it is understandable that women may look to some alternate method of inducing labour.

One American study reported that half of women who reach their due dates attempt to initiate labour through a variety of non-medical techniques. There is a proliferation of DIY methods to induce labour that can be found online, and one of the most common recommendations is to have sex. But does sex initiate labour?

There are biologically plausible reasons why having sex at term may help to speed the arrival of a baby. First, semen is a natural source of prostaglandins, which are used in synthetic form to encourage cervical ripening in preparation for labour. Second, sex plus or minus orgasm has been found to increase uterine activity, and nipple stimulation is also thought to stimulate the uterus to induce labour.

But despite the biological plausibility and popularity in the community, there has been very little scientific evidence so far to support sex as a method of inducing labour.

One study found that sexual intercourse at term was associated with earlier onset of labour. However, when the researchers repeated this study, they found the reverse: women who reported having sex at term were actually less likely to go into spontaneous labour than women who abstained.

A US study confirmed these results and also found no significant cervical changes for women who were sexually active at term compared with those who were not, disputing the cervical ripening hypothesis.

So if there is no scientific evidence to support this method of labour induction, why are more than three quarters of pregnant women aware of this myth and why do almost half of all women believe it?

Well, the thing about being 40 weeks' pregnant, is that sex or no sex, you are likely to go into spontaneous labour at any moment. So it's very easy to mistakenly identify sex as the cause when, in fact, it may be completely irrelevant. Psychological research has shown that once something has happened to us, we are more likely to believe that it is universally true, hence the proliferation of testimonials for this being the cause of labour.

It's also a difficult thing to assess, as sexual activity is hard to uniformly define. Breast stimulation, for example, may or may not be part of sexual activity, and the role of prostaglandins from semen will depend on condom use, volume of ejaculate, and concentration of prostaglandin within the ejaculate.

There are reasons why some women may avoid sex at term, not the least of which is the necessary gymnastic skill. Women who are experiencing abdominal discomfort, mild contractions, or pelvic pressure may be less likely to extend a "come hither" look to their partner, and these symptoms may also indicate labour is imminent. Hence the findings that those who abstain from sex at term are more likely to go into spontaneous labour.

In terms of other labour induction myths, there is also no evidence to suggest that eating spicy food at term can speed the arrival of your baby.

The same goes for castor oil, which is more likely to have you running for the toilet than the delivery suite.

Reportedly, some Native American tribes traditionally believe that a fright can induce labour, and other cultures believe that starving the mother in the last week of pregnancy will encourage the baby to emerge in search of a feed. Aside from the lack of scientific evidence, frightening or starving the baby out really doesn't seem like the kindest way to welcome your bundle of joy to the world.

So it would appear that, in the tradition of the online Chinese baby gender predictor that is right 50% of the time, having sex at term may indeed induce labour, or equally likely, it may not.

Toey even though you can't see your toes? Unless you have a high-risk pregnancy and have been advised to abstain, there is no harm done from sex, curry or both.

This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).