How does an IUD function to prevent pregnancy?

An intrauterine device (IUD) functions primarily by blocking sperm from entering the uterus, which is a critical mechanism in preventing pregnancy. When an IUD is placed within the uterine cavity, it creates a physical barrier that either immobilizes sperm or prevents them from extending through the cervical canal into the uterus and reaching an ovum (egg). This structural obstruction is key to its contraceptive properties, as it significantly reduces the likelihood of fertilization occurring.

Additionally, while some IUDs (like hormonal IUDs) may also influence other mechanisms such as thickening the cervical mucus or affecting the uterine lining to hinder implantation, the primary function of creating a barrier to sperm entry is essential in understanding how the IUD works overall. This barrier method is effective regardless of whether or not ovulation occurs, making it a reliable form of contraception.

Other methods mentioned might play a role in different forms of contraception, but they do not reflect the primary action of an IUD. The distinction in function allows for a clear understanding of its use and effectiveness in preventing pregnancy.