The Intrauterine Device (IUD) is a highly effective, long-acting reversible contraceptive method placed directly into the uterus. The two main types available are the hormonal IUD, which releases a synthetic progestin, and the non-hormonal IUD, which uses copper. As with any long-term medical device, potential users often question the risk of cancer. This article addresses the data surrounding the use of an IUD and the risk of developing ovarian cancer.
Current Research on IUDs and Ovarian Cancer Risk
Extensive epidemiological research and large-scale meta-analyses consistently suggest that IUD use is associated with a reduction in the risk of developing ovarian cancer. Women who have ever used an IUD are less likely to be diagnosed with this cancer compared to women who have never used one. One systematic review and meta-analysis found that IUD use was associated with a 32% lower risk of ovarian cancer incidence.
The statistical findings show a protective association, with the summary odds ratio for ever-use of an IUD and incident ovarian cancer being 0.68. The data gathered for these analyses includes information from thousands of cases and controls across multiple international studies.
Medical bodies and researchers acknowledge this protective correlation, although the exact magnitude can vary slightly between different study designs. For example, some large cohort studies have found a non-significant reduction in the risk of invasive ovarian tumors. Overall, the prevailing evidence supports the idea that IUDs do not cause ovarian cancer but rather appear to offer a degree of protection against it.
Differentiating Risk Based on IUD Type
The two primary IUD types—hormonal and copper—operate through different biological mechanisms. Hormonal IUDs release levonorgestrel, a progestin, which thins the lining of the uterus and thickens cervical mucus. This hormonal action is thought to contribute to a reduced ovarian cancer risk.
The copper IUD does not rely on hormones, instead creating a local inflammatory reaction that is toxic to sperm. Studies suggest that copper IUDs also contribute to the overall observed risk reduction for ovarian cancer.
While some population-based studies have specifically linked the protective effect to the hormonal IUD, other analyses were unable to definitively determine if one type offered a stronger effect than the other. The current scientific understanding is that both hormonal and copper IUDs are associated with a reduced risk of ovarian cancer.
Proposed Biological Protective Mechanisms
The protective effect of IUDs against ovarian cancer stems from distinct biological pathways, depending on the device type. For hormonal IUDs, the localized release of progestin is the primary mechanism. Progestins have an anti-estrogenic effect on the reproductive tract.
The hormonal action is hypothesized to prevent the retrograde flow of menstrual blood, a leading theory for how ovarian cancer begins. Menstrual fluid contains cells that may travel back up through the fallopian tubes, possibly carrying precancerous cells to the ovaries. By thinning the uterine lining, the hormonal IUD reduces the volume of cells available for this backward flow.
For the non-hormonal copper IUD, the proposed mechanism involves a low-grade, localized immune response within the female reproductive tract. The presence of the copper device stimulates the release of immune cells and inflammatory factors. This continuous, mild inflammatory state may enhance “immunosurveillance,” allowing the body’s immune cells to identify and clear any precancerous cells before they can develop into a tumor.
Common IUD Safety Concerns and Side Effects
While the research on ovarian cancer risk is reassuring, individuals considering an IUD should be aware of common non-cancer related side effects. The most frequent reasons for IUD removal are related to changes in menstrual bleeding and cramping. Hormonal IUDs often cause irregular spotting and lighter periods, with some users eventually stopping their periods entirely.
In contrast, the copper IUD may cause periods to be heavier, longer, and involve more cramping, particularly in the first few months. Serious complications are rare but include IUD expulsion and uterine perforation, where the device pokes through the uterine wall.
There is also a small, transient risk of pelvic inflammatory disease (PID), typically confined to the first 20 days after insertion. PID is caused by bacteria introduced during the insertion process. Other common side effects include post-insertion pain, headaches, and for hormonal IUDs, the development of small, usually harmless ovarian cysts.