The problem is that sometimes sperm are released before ejaculation-which is why it doesn't work for all couples. Another flaw is that this method provides no protection from sexually transmitted diseases. It can be very successful, but it also can have a high failure rate. It is acceptable to all cultural and religious groups. The rhythm method makes use of several facts.
Women only ovulate once a month, usually midway between two menstrual cycles.
Sperm, on the other hand, can live for 3 to 5 days after intercourse inside a woman. The safest rhythm method is when the couple abstains from sex until the woman is sure that she has ovulated. Some use the calendar, and try to predict fertile days based on cycle length. Other, more reliable methods pay attention to changes in woman's body, such as cervical mucus. These changes vary with the hormonal condition, which determines the fertile time.