The contraceptive natural methods work on principle of avoiding chances of ovum and sperms meeting. It can be through following methods : 

(1) Periodic abstinence is one such method in which the couples avoid or abstain from coitus from day 10 to 17 of the menstrual cycle when ovulation could be expected. As chances of fertilization are very high during this period, it is called the fertile period. Therefore, by abstaining from coitus during this period conception could be prevented. 

(2) Withdrawal or coitus enterruptus is another method in which the male partner with draws his penis from the vagina just before ejaculations so as to avoid insemination. 

(3) Lactational amenorrhea (absence of menstruation) method is based on the fact that ovulation and therefore the cycle do not occur during the period of intense lactation following parturition. Therefore, as long as mother breast-feeds the child fully, chances of conception are almost nil. However, this method has been reported to be effective only upto a maximum period of six months following parturition. As no medicines or devices are used in these methods, side effects are almost nil. Chances of failure, are also high.