In order to reach high effectiveness rates, hormonal contraceptives rely on two main mechanisms: prevention of the fertilization of a woman’s egg (prefertilization effect), and prevention of the implantation of an embryo by the modification of the lining of the uterus (postfertilization effect). The second mechanism is what we’re concerned with here. If ovulation occurs and if the egg is fertilized by a sperm, which sometimes happens, especially with today’s low-dose pills[iv], the resulting embryo will travel to the uterus and attempt implantation. However, scientific literature shows that oral contraceptives, implants, the shot, the patch[v] and IUDs make the lining of the uterus inhospitable to it. It is also clearly stated in the labels of these contraceptive methods[vi].