IT鈥橲 almost impossible to predict when a woman will be fertile, a study of
200 healthy women has revealed.
Conventional wisdom holds that a woman鈥檚 fertile window鈥攖he six days
before and including ovulation鈥攊s usually midway through the 28-day
menstrual cycle, some time between days 10 and 17. But Allen Wilcox of the US
National Institutes of Health near Washington DC found that this was true of
only 30 per cent of the women (British Medical Journal, vol 321, p
1260). There is even a 1 to 6 per cent chance of becoming pregnant on the day a
period is due鈥攍ong considered one of the 鈥渟afest鈥� days.
鈥淭he fertile window is very difficult to predict,鈥� Wilcox says. 鈥淭he rhythm
method of contraception is certainly not one I鈥檇 want to rely on.鈥�
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