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How do hormonal IUDs prevent 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.

Hormonal intrauterine devices (IUDs) prevent pregnancy through several mechanisms driven by the continuous release of a synthetic progestin hormone.12

These devices function by:
* Thickening cervical mucus: This creates a barrier that prevents sperm from reaching and fertilizing an egg.13
* Thinning the uterine lining: This change makes the uterus less receptive to implantation.13
* Suppressing ovulation: Some hormonal IUDs inhibit the release of an egg by suppressing ovulation, often by decreasing the secretion of hormones like luteinizing hormone and follicle-stimulating hormone.132

By combining these effects, hormonal IUDs are highly effective at preventing fertilization and subsequent pregnancy. It is important to note that while these devices are highly effective forms of birth control, they do not provide protection against sexually transmitted diseases.13