Birth Control Pills
Oral contraceptives (birth control pills) are medications that prevent pregnancy. They are one method of birth control. Oral contraceptives are hormonal preparations that may contain combinations of the hormones estrogen and progestin or progestin alone. Combinations of estrogen and progestin prevent pregnancy by inhibiting the release of the hormones luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the pituitary gland in the brain. LH and FSH play key roles in the development of the egg and preparation of the lining of the uterus for implantation of the embryo. Progestin also makes the uterine mucus that surrounds the egg more difficult for sperm to penetrate and, therefore, for fertilization to take place. In some women, progestin inhibits ovulation.
- Monophasic birth control pills deliver the same amount of estrogen and progestin every day.
- Biphasic birth control pills deliver the same amount of estrogen every day for the first 21 days of the cycle. During the first half of the cycle, the progestin/estrogen ratio is lower to allow the lining of the uterus (endometrium) to thicken as it normally does during the menstrual cycle. During the second half of the cycle, the progestin/estrogen ratio is higher to allow the normal shedding of the lining of the uterus to occur.
- Triphasic birth control pills have constant or changing estrogen concentrations and varying progestin concentrations throughout the cycle. There is no evidence that bi- or triphasic oral contraceptives are safer or superior to monophasic oral contraceptives, or vice versa, in their effectiveness for the prevention of pregnancy.