If the pill is taken during ovulation, it may be too late to stop the ovaries from ovulating because the follicle has reached maturity and will rupture at any time to expel the egg. Therefore, after taking the pill, there is a process of absorption, the drug will play a role, may sometimes be too late, this time the ovaries will still ovulate, the vast majority of the time if the pill is given in accordance with the appropriate time, it will prevent the ovaries from ovulating. One of the effects of birth control pills is to inhibit ovarian ovulation, although there is no inhibition to the case of ovulation; another effect can change the thickness of the endometrium, can prevent the fertilization of the egg to bed, in the clinic can also play a role in contraception. So the pill has double insurance, one is to inhibit ovarian ovulation; the other is to change the thickness of the endometrium, preventing the fertilized egg to bed and contraception.