The "seven before and eight after" theory of safe period contraception (adult novel about sex knowledge)

"Seven before and eight after" is a common way to calculate the safe period for safe contraception, but some women fail in contraception due to their misunderstanding of "seven before and eight after". As the name suggests, most people think that there is no need to worry too much about contraception during the safe period. In fact, this is very wrong. Let’s see what the experts say! The first seven: This is easy to understand. It refers to the seven days before menstruation. This is the relatively safe post-safe period. Basically no one will misunderstand this. The last eight days: refers to the eight days starting from the first day of menstruation, not from the end of menstruation. If a woman starts her menstruation on December 1st and ends on December 6th, then the "last eight" refers to the eight days from December 1st to December 8th, rather than the eight days from December 7th to December 14th which are calculated from the end of the menstruation. In fact, this woman excluded the days of menstruation, and the two days that truly belong to the pre-safe period are December 7 and 8. If a woman's menstrual cycle is less than 26 days, generally speaking, the "first seven" can still be calculated as a safe period, but the "last eight" does not apply. Because safe period contraception is affected by factors such as mood, climate, and environment, ovulation may be advanced, delayed, or even occur extra. Therefore, safe period contraception is not absolutely safe. Therefore, it is not recommended that women use safe period contraception alone.