Marketed as "contraception without contraceptives", Persona, a small hand-held monitor, measures a woman's hormone levels by simple urine tests and tells her when she can make love and yet not conceive by "traffic light" signals.
The monitor displays a green light on the days she is free to have sex without using any form of contraceptive. Conversely, a red light shows the days when she is most fertile.
The method took over 15 years to develop and more than 1,200 women were involved in studies to estimate its efficacy. The studies have found that there is a 95 per cent efficacy rate, which makes Persona as reliable as the condom but less reliable than the Pill.
In the first monthly cycle the woman has to take 16 urine tests which will be used to build up a picture of the woman's individual cycle. From then on she must test herself eight times a month and can typically expect 6 to 10 "red light" days per cycle.
The test measures the levels of two hormones: estradiol and luteinizing hormones [LH], which are markers of the woman's fertile period. The appearance of estradiol marks the beginning of the fertile period whereas the surge in LH indicates the end of the fertile phase.
Women who took part in the clinical trials said that the main advantages of this method were the lack of side effects, ease of use and the freedom to have sex without using contraception. However Persona offers no protection from sexually transmitted diseases such as HIV the virus which causes Aids and if a couple choose to make love on the "red light days" alternative forms of contraception must be used.
"Persona is a real breakthrough in contraception," said Professor John Guillebaud, director of the Margaret Pyke Centre. "It increases women's choice, offering them a method that is not only unambiguous and simple to use, but gives a sense of empowerment, of being in control, a woman working with her own body." But he added that while the Pill was 99 per cent effective, Persona was only 95 per cent and women who felt they must not get pregnant should be aware of the change of a"fivefold degree of efficacy".
Unlike other forms of contraception Persona will not be available free on the NHS but can be bought from Boots stores from today. A starter pack containing a monitor and the first month's supply of 16 test sticks costs pounds 49.95. A month's supply of eight test sticks costs pounds 9.95.Reuse content