How doses oral contraceptives exert contraceptive effiucacy-The mechanism ??

There   are three major   types of OCP   formulations 1) fixed dose combination   , 2) combination phasic and 3) daily progestin only The combination estrogen and  progestin formulations   consistently inhibit the midcycle luteinizing hormone  surge and effectively  prevent ovulation . Several   studies   demonstrated a direct  inhibitory effect  on the pituitary   and the hypothalamus.   The progestin only formulations   have a lower   dose of progestin   than the combined   agents and do not   consistently inhibit   ovulation .

All    formulations act on other   areas of the reproductive  tract by altering the following:  1) Cervical  mucus  making it viscid  thick  and scanty   thus preventing sperm  penetration and inhibiting capacitation of the sperm.2)Decreasing   motility  of the uterus    and oviduct  thus inhibiting ova  and sperm  transport. 3)Diminishing endometrial glandular  production of glycogen   making  less energy  available for the blastocyst to survive  in the uterine cavity. 4)  decreasing  ovarian responsiveness to gonadotropin  stimulation.

Because   the doses of steroids  in currently marked OCs are low  neither  gonadotropin production nor ovarian  steroidogenesis   is completely   suppressed.  Complete   absence of  follicular  activity  as was often noted  during high  dose OC use  no longer   occurs. The magnitude of hypothalamic  pituitary   suppression is unrelated  to the age  of the woman or the duration of steroid   use but   is related   to the potency   of the progestin   and estrogen in the formulation. The magnitude of the hypothalamic  pituitary   suppression is correlated with the incidence   and severity of prolonged amenorrhea   after stopping OCs . After discontinuing current   low dose formulations return  to ovulation is usually  rapid . However   because the suppression is   so quickly reversible    there is less  room for error  when using  current low dose   OCs. Extending  the pill free interval for more  than 7 days   may result in break through   ovulation and pregnancy . Women  should be  advised  that the most important    pills  to remember   to take are  the first  ones of each cycle. The new  low dose OC   Yaz shortens  the pill free interval  to 4 days   to potentially increase  effectiveness with typical use .

 Mode of action as  Contraceptives:-There   are three major   types of OCP   formulations 1) fixed dose combination   , 2) combination phasic and 3) daily progestin only The combination  estrogen and  progestin formulations   consistently inhibit the midcycle luteinizing hormone  surge and effectively  prevent ovulation . Several   studies   demonstrated  a direct  inhibitory effect  on the pituitary   and the hypothalamus.   The progestin only  formulations   have a lower   dose of progestin   than the combined   agents and do not   consistently inhibit   ovulation .

All    formulations act on other   areas of the reproductive  tract by altering the following:  1) Cervical  mucus  making it viscid  thick  and scanty   thus preventing sperm  penetration and inhibiting capacitation of the sperm.2)Decreasing   motility  of the uterus    and oviduct  thus inhibiting ova  and sperm  transport. 3)Diminishing endometrial glandular  production of glycogen   making  less energy  available for the blastocyst to survive  in the uterine cavity. 4)  decreasing  ovarian responsiveness to gonadotropin  stimulation.