During the second half of a woman's menstrual cycle, there is either the implantation of the fertilized egg, or the lining of the uterus will stop growing so it can be sloughed off at menstruation and the cycle starts again. Women who have a 28-day menstrual cycle can only impregnated by intercourse on the eleventh to sixteenth days of their cycle. Sexual intercourse at other times during a woman's menstrual cycle will not result in pregnancy. Not every woman, of course, has a 28-day cycle. That's why ovulation test kits can be so useful.
The ClearBlue Fertility Monitor, for instance, is a method of testing female fertility at home. ClearBlue monitors use a urine sample to measure changes in two hormones, estrogen and luteinizing hormone. Estrogen builds up during the first half of the menstrual period to enable the growth of the lining of the uterus. A woman's estrogen levels peak just before the release of the egg in ovulation. Luteinizing hormone sends signals to the ovaries that enable the release of the egg. Luteinizing hormone levels peak a day or two after the peak of estrogen levels. The ClearBlue Fertility Monitor informs the user when estrogen and luteinizing hormones have peaked so that the couple will know it is time to have intercourse to conceive a child. The advantage of this fertility monitor is that it can be used by women who have menstrual cycles as short as 21 days or as long as 42 days.
Women who have been on the Pill, however, probably will not have hormonal changes picked up by the monitor until they have off the Pill for 2 or 3 months. There are lower-tech methods such as charting temperatures. Which ever method of fertility monitoring the couple chooses, however, the only way to get pregnant fast is to make sure to have intercourse when the woman is at her maximum fertility. The man can make sure he is at his maximum fertility by avoiding ejaculation for 2 to 4 days prior to his partner's likely date of ovulation, just before the middle of her menstrual period.