Q My girlfriend of five years and I are trying to have a baby, but it has been 10 months of trying and that is taking its toll on our relationship. I feel like a turkey-baster on legs, having to "produce" on demand. Sex has become a chore rather than a pleasure and I don't know how long I can do it for. Any suggestions?

A In Breathe: A Guy’s Guide to Pregnancy (Simon & Schuster), by Mason Brown, there is an amusingly twisted little graph that illustrates how the odds of conception are inversely proportional to its desirability. At the peak of the chart are unwed teenage boys who get girls pregnant if they look twice at them. At the base are financially secure married men hoping for children who are doomed to spend their weekends in fertility clinics masturbating into cups.

When you cast you mind back over a sexual history dominated by condom use and finger-crossing, the indignity of “producing on demand” is doubly infuriating. All those university pregnancy scares were wasted angst and now, when you want her to pee two blue lines it refuses to happen.

Though it’s a secret best confined to the eight remaining people in Britain who qualify for a mortgage, it is quite difficult to get pregnant. For every 100 couples having sex two to three times a week, about 30 will conceive within one month, 60 will be pregnant within six months and 85 will have conceived within a year.

When a couple first make the decision to try for a baby there is huge expectation, but by the time that foreplay involves ovulation kits, calendars, secretions and temperature charts, men begin to feel that they are being used. Inevitably this has a deleterious effect on a couple’s sex life. The combined frustrations of paranoia and passion-killing persistence are enough to dampen the enthusiasm of any potential parent, but, if it is any consolation, you and your girlfriend are not at the point where you should be concerned about infertility.

If your girlfriend was on the Pill before you started trying, rule out the first three months because her ovulation would have been all over the place. And if you have been using an ovulation kit and waiting until she has ovulated, you need to pull your timing back by a day or two because sperm can live for several days inside the body. Having sex before ovulation occurs gives the little fellows time to travel up the Fallopian tubes and lie in wait for the egg.

You also need to have sex every other day because storing up sperm for longer than three days is detrimental to its quality. You should be doing everything you can to maximise your chances of conceiving naturally because assisted fertility is a nightmare. If you and your girlfriend went to a doctor tomorrow you would probably be advised to start having tests and, regardless of the results, you would start to believe that there was something wrong. That anxiety would further scupper your chances and you would, as Mason Brown points out, soon find yourself masturbating into a sterile jar in a hospital cubicle.

Infertility is big business in Britain, but Zita West, one of Britain’s best-known fertility experts, admits that 50 per cent of the couples she sees in her practice have nothing wrong with them apart from that they don’t understand ovulation and they don’t have enough sex. So, stop worrying, take a month off work, go on an amazing holiday with your girlfriend and forget about the whole thing.

Three friends of mine who were in the same boat as you did just that and it certainly put the spark back into their relationships. One couple who had given up on IVF went scuba-diving. Another couple who had been trying for more than a year spent the money that they had put aside for IVF on a Caribbean holiday. And a third friend who had not used contraception since she got married two years ago travelled to New Zealand with her husband. I have no science to support it, but all three couples came back with an extra passenger on board.

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