The more frequently you have sex, the more chance you have of getting pregnant. Nobody will be surprised at that - but what is surprising is that, according to various scientific studies, an average couple in Britain having reasonably regular sex have only about an 18 per cent chance of conceiving in any given month.
Interestingly, in New South Wales the chance of getting pregnant each month is significantly higher at about 24 per cent. And that's almost certainly because Australians tend to have sex more often.
In Europe, the French tend to think of themselves as the sexiest nation, but it turns out the average chance of pregnancy per month in Paris (if you are a native) is about 15 per cent. To many Britons, this may be a rather satisfying statistic.
Throughout my career as a professor at Imperial College in London treating people suffering from infertility, I have often wondered how much a couple's physical relationship impacts on their chances of conception.
It was some years ago that I first read that it is not merely the frequency of intercourse that improves a woman's chance of conceiving but also how often she has an orgasm.
Obviously, for men an orgasm is essential for a pregnancy, because without one sperm will not be released. But previously the female orgasm, though highly pleasurable, has often been thought of as being biologically useless.
Certainly, this link between satisfying sex and conception is an interesting one.
But it was with some trepidation that I first researched this idea 20 years ago. Back then, I organised a study of infertile women attending a clinic at Hammersmith Hospital.
It was one of the trickiest and most delicate pieces of research I ever conducted, as it required considerable tact and sensitivity.
We had to ask patients about the most intimate aspect of their sexual relationship, particularly about how satisfying it was and how often they had an orgasm.
One of my female medical colleagues conducted much of this questionnaire in the belief that women would be more likely to speak candidly to her.
Over many months, we built up a picture from conversations with nearly 1,000 female patients. When analysing the answers, we divided our patients into three main groups.
The first group were women who had entirely healthy and apparently fertile male partners, but despite extensive investigation had no diagnosable cause for their infertility.
The second group were women with damaged or blocked Fallopian tubes, which meant the sperm could not meet the egg and therefore fertilisation could not take place.
And in the third group were women who did not ovulate because of hormonal problems and those whose partners had a low sperm count.
It turned out that the women in the first group with completely unexplained infertility tended to say they had a rather unsatisfying sexual relationship and seldom or never had an orgasm.
These women were medically entirely normal and our tests failed to find an explanation for their childlessness.
But it was astonishing to find out that women who were infertile because they had damaged or blocked fallopian tubes were often more likely to have an orgasm than those patients in the other two groups.
How could we account for these two findings in a scientific way?
One theory is that the muscles of the vagina and the womb contract, sometimes quite vigorously, during orgasm and that way more sperm enters the uterus.
Then, after a period of relaxation, the sperm are retained. We do know that, during orgasm, a hormone is released - oxytocin, which, among other things, is associated with extreme pleasure. This hormone is also important in producing contractions of the womb.
As for why it was that a number of our patients with tubal damage reported having a particularly pleasurable sexual relationship, well, that could be down to the fact that most tubal blockage results from infection.
It is possible that the suction effect of orgasm may not just gather sperm into the uterus but also bacteria. While bacteria cannot survive long in the environment of the womb, if passed rapidly into the tubes they may set up an infection.
Evolutionary biologists tend to be rather more prosaic about the female climax.
They often suggest that the pleasure associated with having an orgasm simply encourages a woman to have more sex.
And the more she does the more likely it is that she will become pregnant and continue to ensure the survival of our species.
Linking fertility and sexual enjoyment is highly controversial scientifically, not least because many women seldom have an orgasm and many who have never had one often get pregnant without difficulty.
I am quite attracted by the theory that contractions of the womb and the fallopian tubes may help pregnancy. But after much agonising, I decided to not submit my research for publication in a scientific journal.
I was concerned that many infertile patients already feel guilty about their failure to conceive.
This guilt is not rational, but it is understandable. They feel they have failed their partner or that they may have damaged themselves in some way - or that they may be causing their own infertility.
Publication of an inconclusive study like this might encourage infertile patients to feel even worse about themselves when there was no clear evidence that orgasm improves fertility in the majority of women.
All, this was only a questionnaire based on conversations with patients. No matter how carefully done, it was possible our patients were not always being totally candid about this intimate aspect of their lives.
Ultimately, we shelved our study. We could not prove what we thought we might have found and we needed to do more work on our theories.
But other research areas were more pressing and we never returned to this vexed issue.
I still feel that doing more research in this difficult area would be worthwhile.
Two decades on, we are much more open about the issues surrounding infertility.
Hopefully some sensitive and keen researchers may consider revisiting this important aspect of human sexuality.
Febby Indra on 
11:44 AM
