<unk><unk><unk>  are various<unk>  of estimating a woman's likelihood of fertility,<unk>  on a record of the length of previous menstrual cycles. Various<unk>  are known as the Knaus–Ogino<unk> and the rhythm<unk>  The standard days<unk> is also considered a<unk><unk> <unk>  because when using it, a woman tracks the days of her menstrual cycle without observing her physical fertility signs. The standard days<unk> is<unk>  on a fixed formula taking into consideration the timing of ovulation, the functional life of the sperm and the ovum, and the resulting likelihood of pregnancy on particular days of the menstrual cycle. These<unk>  may be used to achieve pregnancy by timing unprotected intercourse for days identified as fertile, or to avoid pregnancy by avoiding unprotected intercourse during fertile days. The first formalized<unk><unk> <unk> was developed in 1930 by John Smulders, a Catholic physician from the Netherlands. It was<unk>  on knowledge of the menstrual cycle. This<unk> was independently discovered by Hermann Knaus (Austria), and Kyusaku Ogino (Japan). This system was a main form of birth control available to Catholic couples for several decades, until the popularization of symptoms-based fertility awareness<unk> . A new development in<unk><unk><unk>  occurred in 2002, when Georgetown University introduced the Standard Days<unk>  The Standard Days<unk> is promoted in conjunction with a product called CycleBeads, a ring of colored beads which are meant to help the user keep track of her fertile and non-fertile days.
Calendar-based contraceptive methods
Combined injectable birth control
Long-acting reversible contraception
Heat-based contraception
Safe sex
Combined oral contraceptive pill
Contraceptive mandate
Extended cycle combined hormonal contraceptive