Aclient states that she wishes to use the calendar method of birth control. the nurse concludes that the client understands how to calculate the beginning of the fertile period when she makes which statement?
1. i will subtract 11 days from the length of my longest cycle
2. i will subtract 18 days from the length of my shortest cycle
3. i will abstain from having sex after the 10th day of my cycle
4. i will abstain from sex from the 10th day before the middle of my average cycle

2. I will subtract 18 days from the length of my shortest cycle

Explanation:

The calendar method or the Ogino-Knaus method is a natural method of birth control. It was developed in 1924 by the Japanese gynecologist Kyusaku Ogino, and perfected by the Austrian doctor Hermann Knaus in 1928. It consists of counting the days of the menstrual cycle and choosing the appropriate days of the woman's sexual relations to avoid getting pregnant.

In order to calculate the first day in the cycle in which the woman is fertile, the woman should subtract 18 from the number of days of her shortest menstrual cycle in the six month period. For example, for a woman whose menstrual cycle extends between 25 and 32 days, it is estimated that she is infertile the first 7 days of her cycle (25 - 18 = 7), is fertile between days 8 and 20 and becomes infertile again on day 21 (32 - 11 = 21).