The date that the woman will next release a mature ovum is estimated on the basis of the average length of her menstrual period, and the time of her last period. If successful, then the technique prevents live sperm and a live ovum from being present in the fallopian tubes simultaneously. Any number of factors, including stress, can introduce irregularity into the timing of the release of the ovum, and make the method quite unreliable. The woman observes her vaginal discharge on a daily basis. There are subtle changes in texture, quantity and color which indicate when ovulation is happening.
Sexual intercourse is avoided for a while at that time.
The woman measures her body temperature. There is a small rise in temperature after ovulation. Sexual intercourse is avoided for a while at that time. The condom is the most common mechanical contraceptive. It is a latex sleeve that is placed over the erect penis.