Sex more likely during women's fertile phase

The research suggests that having unprotected sex once is more likely to result in pregnancy than previously thought.

Women are significantly more likely to have sex during the fertile part of their monthly cycle, suggests new research.

"If you're a couple trying to get pregnant, that's great news. There's a hidden biological process working in your favour," says Allen Wilcox, a reproductive epidemiologist at the US National Institute of Environmental Health Sciences in Durham, North Carolina, and lead researcher of the study.

"If you are not trying to pregnant the news is not so good," he told New Scientist. The work indicates that having unprotected sex once is more likely to result in pregnancy than previously thought.

The underlying reason for the coincidence of intercourse and heightened fertility is not clear. Previous research suggests women feel sexier in the days before ovulation, which may increase their own libido or make them more attractive to their partners. And men have been found to be more attentive to their female partners around ovulation.

However, those studies did not determine whether these loving feelings actually resulted in more sex. And Wilcox's group have some evidence that sex may actually act as a trigger for ovulation, and not the other way around. "But that would need to be confirmed in a larger study," he says.

Timing sex

There has been plenty of anecdotal evidence that couples were friskier at the fertile time of the month. But what little research had been done in this area focused on couples who were trying to conceive, and therefore might have been timing sex to improve their odds. Instead, Wilcox's study focused on 68 sexually-active women who were using strong methods of birth control - they had an intrauterine device or had been sterilised by tubal ligation surgery.

But even though they had no plans to have a baby, the women were 24 per cent more likely to have sex in the six days leading up to ovulation, the most fertile time of their menstrual cycle.

"There have been hints of this before. But Wilcox has produced the first well documented study of this effect," says Marcelle Cedars, a reproductive endocrinologist at University of California, San Francisco Medical Center.

The study was not designed to determine if the boost in sexual activity was spurred by ovulatory events or the other way around. But Wilcox's team did discover an intriguing pattern.

Making whoopee

Couples were most likely to make whoopee on the weekend, presumably because the working week is not as accommodating to romantic plans.

Women whose sexual schedule was twice as busy between Friday and Sunday compared to the rest of the week, were also significantly more likely to ovulate a day or two later. This suggests that love making may have hastened ovulation, something known to occur in other mammals.

But Cedar is skeptical that sex causes ovulation in people. "I think it's more likely to be a change in desire of either the women or her partner," she says.

Wilcox adds that further studies will be necessary to study the effect and rule out that other weekend factors might hasten ovulation. "Patterns of sleep change, stress levels go down, so sex isn't the only one."

Source: Newscientist.com

Journal reference: Human Reproduction (DOI: 10.1093/humrep/deh305)