An intrauterine device (IUD) is a small, T-shaped piece of plastic placed inside the uterus to provide long-acting reversible contraception. This method is highly effective at preventing pregnancy and has seen a substantial increase in use globally. As a medical device that remains in the body for years, questions often arise regarding its long-term health effects, including any potential link to cancer. Current scientific evidence provides a clear answer: the IUD does not increase the risk of developing ovarian cancer.
IUDs and the Reduction of Ovarian Cancer Risk
Extensive research, including large-scale meta-analyses, has found that IUD use is associated with a significantly reduced risk of ovarian cancer. Studies combining data from multiple cohort and case-control studies consistently demonstrate this protective effect. Women who have ever used an IUD are less likely to develop ovarian cancer compared to those who have never used one.
This reduction in risk is estimated to be between 15% and 32% for all types of IUDs combined. One large meta-analysis found that IUD users were approximately 32% less likely to develop the disease. This preventative association is medically significant because ovarian cancer is often detected at a late stage. The data indicates that the device offers a degree of protection against its development.
The protective association is similar in magnitude to the effect seen with oral contraceptive pills, which are well-known to lower ovarian cancer risk. Researchers are investigating the underlying mechanisms to understand how a device placed in the uterus can affect cancer development in the ovaries. This discovery suggests that the IUD provides substantial non-contraceptive health benefits.
Proposed Biological Reasons for Protection
The protective effect of the IUD is thought to stem from distinct biological pathways, depending on the device type.
Hormonal Mechanism
For levonorgestrel-releasing IUDs, the localized delivery of progestin provides a hormonal mechanism of protection. This hormone induces changes in the uterine lining, suppressing endometrial proliferation similar to how hormonal contraceptives reduce risk.
Inflammatory Mechanism
The local inflammatory response triggered by the presence of any foreign body, including both hormonal and copper IUDs, represents a non-hormonal mechanism. The device creates a low-level, localized immune reaction in the uterus, increasing the number of immune cells. This heightened immune surveillance may help clear pre-cancerous or malignant cells before they can migrate to the pelvis.
Mechanical Barrier
A separate, mechanical theory known as the ‘tubal flushing’ hypothesis also contributes to protection. Many ovarian cancers are believed to originate in the fallopian tubes, and the IUD may act as a physical or functional barrier. The IUD might prevent the retrograde flow of potentially carcinogenic agents or cells from the vagina and cervix up through the uterus and into the tubes.
How Different IUD Types Affect Risk
The two main types of IUDs are the levonorgestrel-releasing (hormonal) and the copper-containing IUDs, and their cancer-reducing effects differ slightly. Evidence for the hormonal IUD is generally stronger and more consistent across studies because it benefits from both the localized hormonal effect and the foreign-body inflammatory response.
Studies focusing specifically on the hormonal IUD show a pronounced reduction in ovarian cancer risk. The continuous progestin release provides an anti-estrogenic environment that inhibits cell growth and turnover. While the copper IUD lacks the hormonal component, it still offers some degree of protection.
The copper IUD’s protective trend is attributed primarily to the non-hormonal, inflammatory mechanism. The presence of the copper wire and the device itself induces the local immune response and may contribute to the mechanical barrier effect. Both types of IUDs are associated with a reduced incidence of ovarian cancer.
Established Risk Factors for Ovarian Cancer
Understanding the factors that influence ovarian cancer risk provides context for the IUD findings. The most significant established risk factor is a person’s genetic makeup, particularly inherited mutations in the $BRCA1$ and $BRCA2$ genes. These mutations substantially increase the lifetime risk of developing the disease, as do inherited conditions like Lynch syndrome.
Age is a non-modifiable factor, with risk increasing significantly after menopause. Reproductive history also plays a role; never having given birth (nulliparity) is associated with a higher risk. Early onset of menstruation or late onset of menopause are also established risk factors.
Certain medical conditions, such as a personal history of endometriosis, are linked to an increased risk of developing specific types of ovarian cancer. A strong family history of ovarian, breast, or colorectal cancer is also an indicator of potential risk. These factors help clinicians determine an individual’s baseline risk.