Combination birth control methods (such as the birth control pill, the patch, and NuvaRing) prevent ovulation, and progestin-only birth control (like Depo-Provera, the minipill, Mirena, Nexplanon, and Skyla) can also do this.
How Does Birth Control Stop Ovulation?
Hormonal birth control prevents ovulation by inhibiting the signal that triggers the two key hormones that are involved in ovulation: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These two hormones will begin to be produced if your body notices a shortage of estrogen and progesterone.
Hormonal birth control provides just enough synthetic estrogen and progesterone hormones to prevent the stimulation of FSH and LH production.
Normally, the hypothalamus in your brain detects when your estrogen levels are low, typically during the first days of your menstrual cycle. During certain phases of your menstrual cycle, your hypothalamus releases gonadotropin-releasing hormone (GnRH). This is the hormone that signals the pituitary gland in your brain to make FSH and LH. Since birth control prevents the hypothalamic message from being sent to your pituitary gland, the pituitary gland does not produce FSH. Without the release of FSH, there is no signal to trigger the growth and development of egg follicles in the ovaries. Ovulation normally takes place in response to a surge of LH that triggers an egg to be released from the ovary. With hormonal birth control, there is no LH surge, so the egg’s release is not activated and ovulation does not take place.
Hormonal birth control basically keeps you in the same phase of your menstrual cycle on a continuous basis, skipping the release of GnRH and preventing ovulation from taking place.
Why It Matters Whether Birth Control Stops Ovulation
For some women, their personal ethics, morality, or religion guide whether they choose a birth control method that inhibits ovulation, fertilization, or the implantation of the fertilized ovum. For those who believe life begins when the egg is fertilized (at conception), preventing the release of an unfertilized ovum could be acceptable, but preventing pregnancy after the egg is fertilized might not be acceptable.
Hormonal birth control prevents pregnancy in three main ways:
Stops ovulation so an egg isn’t released Thickens cervical mucus so that sperm cannot enter the uterus and fallopian tubes to fertilize an egg Thins the uterine lining so that a fertilized egg can’t implant and grow
Combination hormonal birth control prevents ovulation. Progestin-only birth control can prevent ovulation in about 40% of women, but this is not the main mechanism by which it prevents pregnancy—its other effects on the cervical mucus and uterine lining act to prevent pregnancy if ovulation occurs.
After a week of taking pills, combined birth control pills should start to prevent ovulation. If you started the pill pack at the beginning of your cycle, you will not ovulate. If you took the first pill after day seven of your cycle, you may still ovulate the first month, but you shouldn’t ovulate after that, provided you take them daily as prescribed.
