A new watch-like device can now predict a woman's most fertile time of the month.
'For women, knowing the days before ovulation not only lowers stress levels, but it increases her chances of getting pregnant,' say developers of Health Watch Systems.
A woman's 'fertility window' starts four days before ovulation and continues until the day after. Intercourse on the day of ovulation gives the highest chance of getting pregnant, but intercourse up to four days before ovulation can still result in pregnancy because sperm can survive for as long as six days in the reproductive tract, reports the Daily Mail.
The technology, which has been approved by the U.S. Food and Drug Administration, is based on the idea that levels of a number of salts in a woman's sweat, including chloride, change during the menstrual cycle.<b1>
The device uses sensors to detect chloride levels which are low at the start of the cycle and peak three times during it.
The device works out the normal chloride level for each user, then predicts ovulation. It can detect the chloride surge three days before the monthly oestrogen surge, four days before the increase in luteinizing hormone (which helps regulate the menstrual cycle and egg production) and five days before ovulation.
The device is worn on the woman's wrist while she sleeps and can be programmed for cycles ranging from 20 days to 39 days. A clinical trial is looking at the ability of the device also to predict ovulation in women taking clomiphene citrate, medication used for women who do not ovulate on their own or ovulate irregularly.
Female fertility declines with age, but with regular unprotected intercourse, 94per cent of fertile women aged 35, and 77 per cent aged over 38 years will conceive after three years of trying.