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Why does forgetting birth control pills increase the chance of pregnancy?

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Blister pack of 28 oral contraceptive pills arranged in four rows, with 21 white active pills followed by 7 orange inactive pills. Arrows indicate the order for taking pills. — birth control A 28-day package of birth control pills.

Birth control pills function by delivering synthetic steroid hormones that suppress the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary gland. Under normal conditions, these hormones trigger the ovaries to release a mature egg, a process known as ovulation.12

By consistently maintaining these hormone levels, the medication prevents the body from signaling the release of an egg, thereby significantly reducing the likelihood of fertilization. When a dose is missed, the concentration of these hormones in the body drops, which may allow the pituitary gland to resume the production of FSH and LH. This can lead to the resumption of ovulation, removing the primary barrier to pregnancy. Additionally, for progestin-only pills, missing a dose may cause the cervical mucus to thin, making it easier for sperm to reach an egg. Consistent daily use is essential to maintain the hormonal suppression required for maximum effectiveness.12