THE TEMPERATURE chart showed that today was the optimum window of opportunity. The conditions for conception looked good. Jack hadn't masturbated for three weeks. The only problem was that Joanne, his wife, was at a seminar, 200 miles away in Manchester. The drive from London was a nightmare, with motorway snarl-ups, dense fog and an hour in a Byzantine one-way system searching for Joanne's hotel.

By the time Jack made it he was in no mood to perform. 'I was too exhausted to do anything. Joanne was mad as hell, but there's always next month,' he says.

'Next month' has become a familiar phrase for Jack and Joanne Wallace since they started trying for a baby two years ago. Of the estimated one in eight couples who have problems conceiving, they are among the 28 per cent who fall into the 'unexplained infertility' category - there is no physical reason for their childlessness. But the Wallaces have discounted artificial fertilisation techniques and are doggedly following their GP's advice to 'keep trying'.

And boy, do they try. One bedroom wall, plastered with charts recording Joanne's body temperature and the related rise in progesterone, looks like a statistician's office. The bathroom cabinet is crammed with pregnancy and ovulation tests, mineral supplements and vitamin pills. Jeans or any other crotch- cramping outfits have been banished from Jack's wardrobe and luxurious hot baths are history; he takes lukewarm showers (even in winter) and often splashes cold water on to his testicles in order to keep his sperm cool. 'We will try anything once if it isn't painful or dangerous,' says Joanne.

Jack abstains from masturbation, especially in the days leading up to ovulation, because he believes frequent ejaculation will sap his sperm count. The post-coital cigarette and cuddle are also out. Jack gave up smoking after he learnt it could damage sperm and Joanne hasn't time because immediately after sex she stands on her head in the hope that gravity helps the sperm on their journey. She can now manage five minutes upside down before the blood drains to her head.

Spontaneous love-making is a rare thing in their marriage and sex is limited to the missionary position with a cushion under Joanne's bottom to ensure all the semen that comes out goes in. 'I'm not sure we make love any more, it's so mechanical. Everything is geared towards that one day in the month,' complains Joanne. 'Sex for us now means thermometers, testing kits and dangling my legs in the air. It would be funny if it wasn't so serious.'

According to John Dixon, director of Issue, part of the National Fertility Association, couples such as the Wallaces may eventually conceive, but why it takes so long is often inexplicable. 'Although some people swear by outlandish endeavours, in many cases pregnancy can't be attributed to any one thing,' he says.

Such couples are often susceptible to suggestions from spiritual and philosophical advisers, no matter how unscientific or unproven. Alex and Julia Jackson were labelled 'unexplained infertility' three years ago, although Alex's sperm count is on the borderline for fertile males: 50 million sperms per millilitre. A homeopath advised Julia to give up coffee because the effect of the herbs he recommended would be dissipated by caffeine. 'I had herbs to warm my womb, herbs to lower my blood pressure, herbs to relax me . . . I'd never had so many pills or treatments in my life,' says Julia.

Sometimes she wrapped a warm stone in a towel and placed it on her navel to relax her before going to bed. 'It got to a point where it was taking longer to prepare for sex than the act itself.'

The Marshalls, Alan and Caroline, also resorted to homeopathy, but after two years they went a step further by approaching a practitioner of Feng Shui, the ancient Chinese study of energy lines. He sketched the layout of rooms, windows and doors, moving certain objects - potted plants, wooden drawers, a sofa, a collection of stones Alan had found on a Moroccan beach and an electric fire - to 'balance the energy' within the flat.

The Marshalls were surprised to learn that their bedroom was 'completely inappropriate' and were encouraged to have sex in the kitchen. 'You can imagine how romantic that was, making love next to the washing up,' says Caroline. 'It was also uncomfortable because we had to do it on the kitchen table. We felt ridiculous and kept bursting out laughing.'

The Marshalls moved to the lounge when their adviser returned about a month later to rearrange the furniture. They're now back in the bedroom for the sake of their aching backs.

After four years of trying to start a family, Jane Markham sought alternative treatments because she didn't want to be 'pumped full of hormones or other drugs'. Jane became obsessed with the colour red after a therapist told her it was her 'natural colour' and that getting close to it would increase her fertility. She bullied her husband, Richard, into decorating the bedroom with a garish red wallpaper and she dyed their linen scarlet. 'I even started wearing horrible red bras and knickers,' she says.

Richard, who has a slightly lower than average sperm count, was willing to indulge Jane because he felt he was the 'guilty party'. But he drew the line at fitting red light bulbs in the bedroom. 'The place was beginning to look like a brothel,' he says. 'I wanted children as well, but there was a limit.'

One weekend an exasperated Richard repainted the bedroom a subtler shade. The next day the couple jetted off to Jamaica to consider their prospects for adoption. 'To be honest we had given up on having children, but I think the holiday and the thought of adopting a child relieved a lot of the tension we had been living under,' says Jane. They are expecting their first baby in May.

Some names have been changed.