Yes, a proper understanding of menstrual cycle can help immensely in family planning. This method is known as natural method of birth control. The menstrual cycle consists of four phases, the third phase known as ovulatory phase occurs on about 14th day of the menstruation. Hence, avoiding or abstaining from coitus from days 10 to 17 of the cycle reduces the chances of fertilisation as ovum survive for about 1-2 days and sperms survive for about 3 days. So, temporary avoidance of sex during this phase will help in family planning.