Yet how many will seriously consider natural family planning, and how many will be offered it as an alternative by their GPs or family planning clinics?
Natural family planning (NFP) has come a long way since the days when doctors dismissed it as "Vatican roulette". Women no longer merely mark off safe and unsafe days on a calendar, based on a guess as to when they will ovulate. Instead, they learn how to become tuned into their bodies, using a range of physical symptoms, including temperature changes and observation of cervical mucus, to pinpoint ovulation and the fertile and infertile phases in their cycle.
Only 1 per cent of women use this method - comparable to the numbers using caps, diaphragms or injectable contraceptives, says the FPA. Seventeen per cent use condoms, 5 per cent IUDs, 3 per cent withdrawal and 25 per cent take the Pill. Studies show, however, that NFP works as well as other contraceptive methods, provided women are well motivated and well taught.
Even so, as Bob Ryder, consultant physician and endocrinologist of the City Hospital Trust, Birmingham, says: "NFP has an image problem in the medical and lay world. If you ask your doctor about it, you are likely to be told, 'You don't want to use that - you'll get pregnant'. Yet that attitude is based on out-of-date information."
Dr Ryder, who has worked in this field since the mid-Seventies, has collected data on all NFP studies so far reported in the Nineties. Of the 11 studies, only three reported pregnancy rates greater than 5 per cent. In the UK the rate was 2.7 per cent and in Belgium 1.7. These results compare favourably with reported pregnancy rates of between 0.18 per cent and 3.6 for artificial contraceptive methods in well motivated couples.
Women using NFP learn to interpret the changes in their cervical mucus. After a period there is often little mucus; it then becomes white and cloudy and, as ovulation approaches, transparent and stretchy. After ovulation, the mucus becomes white and cloudy again. Research being carried out in Sweden confirms that the changes in the appearance of the mucus are a reflection of the complex role cervical mucus plays in fertility. "It has several components with different functions, which we are now becoming more aware of," says Dr Ryder. "That is why mucus is such a reliable indicator."
Even so, most proponents of NFP agree that the method - which requires a couple to abstain from intercourse or use barrier methods in the fertile phase - works best if taught by someone experienced. Critics say this is expensive and time-consuming.
Jane Knight, a practice nurse in Oxford, does not agree. She carried out a GP study in 1990 in response to the increasing number of people wanting to use NFP. "We found that the average couple of normal fertility needed four hours of total teaching time spread over monthly intervals, although more time was needed for people with special needs, such as breast- feeding mothers, women coming off the Pill or women who were pre-menopausal.
"The cost for the first year was comparable to the cost of prescribing the Pill, but if the couple continued to use NFP, the costs were really low - and that's not taking into account any hidden costs, such as infection or tubal damage from an IUD. The trouble is, there is no funding coming into NFP. Unlike the Pill, there are no drug companies behind it."
Even so, an increasing number of family planning clinics and practice nurses are being trained in NFP. Colleen Norman, NFP tutor and director of the Fertility Education Trust, says: "Of course, something is easier when someone shows you how to do it. It's like the difference between following a recipe out of a cookery book or watching Delia Smith on television. But there aren't enough teachers at the moment, so we have to make DIY methods better."
Mrs Norman has produced simplified charts for women to use, based on the seasons, with winter representing the barren phase and summer the period of peak fertility. Her new book, Understanding Fertility, will be published in the new year.
Meanwhile, the Fertility Awareness Kit, launched in February and approved by the FPA, has already sold more than 10,000 copies. The kit, created by Andrew Hall, consists of a video, a digital thermometer and a book of charts.
Mr Hall says: "We are now talking to doctors and family planning clinics. We want the kit to be prescribed in the same way as any other contraceptive. There is tremendous ignorance among the medical profession about NFP. The point we are making is that it is no longer a choice motivated by dogma, it's motivated by science. It offers the same sort of reliability as any method bar sterilisation and we are offering a technological approach."
Many people involved in NFP, however, agree that the real breakthrough in terms of technology will come when Unipath launches its hand-held fertility monitor next year. The monitor, which looks rather like a felt-tip pen, detects chemical changes in urine that relate to hormonal changes in the body. Trials are already under way in Britain and the results are being analysed by Professor Robert Snowden at Exeter University. He says: "We are carrying out two studies: one is about effectiveness - does it work in the real world? The other is about acceptability - how couples feel about using it. This is the one kind of contraception, after all, that does require the commitment of two people."
The 'Fertility Awareness Kit', price pounds 19.99, is available by mail order from the FPA (01865 749333) and in some high-street chemists.