Rhythm methods of contraception depend on periodic abstinence from intercourse 'during times of the menstrual cycle when fertility is most likely. These methods are the only methods of birth control approved by the Roman Catholic Church, which considers them "natural" rather than "artificial."

The calendar method involves identifying "safe days" in the menstrual cycle (days where intercourse will not lead to pregnancy) based on the lengths of previous cycles. The underlying assumption is that ovulation will occur approximately fourteen - days before the start of the next menstrual period. Careful hormone studies of the menstrual cycle, however, indicate that this assumption is not always correct.

To calculate the "unsafe" (fertile) period, a record must be kept of the length of each menstrual cycle for a minimum of six months. The first day of the unsafe period is determined by subtracting 18 from the length of the shortest cycle, and the last, day of the unsafe period is found by subtracting 11 from the number of days in the longest cycle. For example, if a woman's shortest cycle is 26 days and her longest is 32 days during her "record keeping" time, she must abstain from intercourse beginning on cycle day 8 (26 - 18 = 8) and continue abstention until day 21 (32 — 11 = 21). Thus, the unsafe days would be days 8 to 21, inclusive, a time of 14 days when intercourse would not be permitted.

The temperature method involves daily recording of the basal body temperature (BBT) to pinpoint the time of ovulation. Intercourse is not allowed from the day menstrual flow stops until two to four days after the temperature rise. (If no temperature rise is detected in a full menstrual cycle, which sometimes happens, users of this method must observe total abstinence from sexual intercourse.)


Men's Health Erectyle Dysfunction