Copper IUDs primarily work by disrupting sperm mobility and damaging sperm so that they are prevented from joining with an egg. Copper acts as a spermicide within the uterus, increasing levels of copper ions, prostaglandins, and white blood cells within the uterine and tubal fluids.[10][16] The increased copper ions in the cervical mucus inhibit the sperm's motility and viability, preventing sperm from traveling through the cervical mucus, or destroying it as it passes through.[17]Copper can also alter the endometrial lining, but studies show that this alteration can prevent implantation, but not disrupt implantation.[18] Copper IUDs have a first year failure rate ranging from 0.1 to 2.2%.[19]