• Fertility awareness–based methods prevent pregnancy by changing sexual behaviour during the woman's fertile time. For example:
• Abstaining from vaginal intercourse — other sexual activity (without vaginal intercourse) may continue.
• Using a barrier method, e.g. condoms.
• Using the withdrawal method (coitus interruptus) — the least effective contraceptive method, and therefore not recommended.
• There are several ways to tell when the fertile time begins and ends, including:
• Calendar calculation. The woman can count the days from the start of the menstrual period, to identify the start and end of the fertile time. When the fertile time begins and ends depends on the length of previous menstrual cycles.
• Cervical secretions. The woman can look and feel for cervical secretions, which can be just a sense of vaginal wetness. Cervical secretions are present during the fertile time.
• Basal body temperature. The woman can monitor her resting body temperature every day. A slight rise in temperature that persists for 3 days indicates that the fertile time has ended.
• Feel of the cervix. The woman can monitor changes in the cervix. As the fertile time begins, the opening of the cervix feels softer, opens slightly, and is moist. When not fertile, the opening is firmer and closed.
• Hormone levels in the urine. The woman can use a device to monitor changes in hormone concentrations in the urine.
• The fertile time is more accurately estimated by a combination of methods than by any single method.

[Hatcher et al, 1997a]