These are methods that, with various systems, identify the days corresponding to the "fertile window": avoiding sexual relations in those days it should be possible to avoid a pregnancy. "Fertile window" means the fertile days of the female cycle, corresponding to the day of ovulation and to the 5 days preceding it: in fact, while the egg has a survival of only one day, the spermatozoa, once penetrated into the genitals female, can live up to 5 days. Although the central days of the cycle are – probably speaking – the most fertile, a recent study has shown that every day of the cycle, with greater or lesser probability, could fall back into the fertile window.
Pros: absence of contraindications and side effects; these methods are the only ones approved by the Catholic Church. Cons: they are not simple or comfortable to use; a trial period of a few months is needed to familiarize yourself with the method and observe the characteristics of your cycle; difficult and unsafe to use when the cycle is irregular; there may be confounding factors (the temperature can rise because you have a fever, vaginal discharge can increase or change characteristics in the presence of an "infection"); systems that use computers, however safer, are quite expensive; free relationships can be practiced only after ovulation onwards (around 12-13 days a month): on other days you must abstain or use other contraceptives; security is not high, even when these methods are used correctly.
Detection of the fertile period