When a woman keeps track of her menstrual cycle and has unprotected sex only during the “safe” (or infertile) days, when it is less likely that she will get pregnant.
With typical use, between 12 and 25 women in 100 (12 to 25%) will become pregnant in one year, depending on the method. With perfect use, between 2 and 9 women out of 100 (2 to 9%) will become pregnant in one year.
It’s free and there are no devices to deal with. There are no side effects, except having to go without sex or use a barrier method for several days before and after ovulation (when it is possible for a woman to get pregnant).
Doesn’t protect against STDs including HIV. Predicting when a woman will ovulate is not easy, and sperm can live inside a woman’s body for days. Women have to keep careful track of their vaginal mucus, menstrual cycle, and/or body temperature beginning several months before they can start relying on this method. Because it’s difficult to accurately track fertility patterns, there are a lot of accidental pregnancies.
How To Get It
Women will need good instruction–a class or health care provider–and several months of charting before they begin to rely on this method.