•When a girl child is born, she has thousands of cells or ova in her two ovaries. Each egg is the size of one grain of sand. The tiny dot in the two balls are the egg. The two balls are the ovaries.

•Each month, one egg _ the big black dot ripens and leaves the ovaries. This is ovulation.
•The egg is picked u by the broad end of the fallopian tube and starts moving towards the uterus, the V-shaped area. At the same time, the uterus starts getting ready for the egg by thickening its inner lining.
•An egg can grow into a baby only if it meets a sperm cell from a male. If the egg and the sperm meet, a woman becomes pregnant.
•If the egg is not fertilized by a sperm, the lining is not needed and breaks down.
•The lining, tissue and the egg flow out of the uterus through the vagina and leave the body. This is menstruation.
Menstruation occurs approximately 14 days after ovulation, if the egg is not fertilized. Menstrual periods may last 2-8 days; the average menstrual period last 4-6 days. The menstrual cycle occurs every month until a woman goes through menopause. It also stops during pregnancy and starts after the baby is born.

How to Calculate Your Menstrual Cycle

In the middle of the menstrual cycle, and between monthly bleedings, a woman should assume that there are 12 days when she could become pregnant.

•These fertile days are difficult to predict exactly because a woman’s menstrual cycle may vary slightly from month to month.
•However, these fertile days will be immediately before and around the time of ovulation; when an egg is released by an ovary into a fallopian tube.
•If a woman has 28 days menstrual cycle, ovulation will take place midway through her cycle; around day 14.
•Sperm can survive in her reproductive tract for up to 5 days and the woman’s egg can survive not more than 24 hours after ovulation.

Thus, she could become pregnant if unprotected sex takes place either 5 days before ovulation or the day of ovulation. This is a 6-day interval that begins around day 9 and ends around day 14 of an average 28-day cycle; It occurs on the exact same day of every menstrual cycle even if they are the same length.
Without knowing the exact day of ovulation, it is hard to identify the exact days when pregnancy will be possible. Therefore, a woman should assume there are not 6 but 12 days in the middle of her menstrual cycle when she could become pregnant. These 12 days account for the 6 fertile days that occur in the shortest as well as the longest menstrual cycles.