A diagram showing a<unk> in place in the uterus. The<unk> s primary mechanism of action is to prevent fertilization.Active substances released from the IUD or IUS, together with products derived from the inflammatory reaction present in the luminal fluids of the genital tract, are toxic for spermatozoa and oocytes, preventing the encounter of healthy gametes and the formation of viable embryos. The current data do not indicate that embryos are formed in IUD users at a rate comparable to that of nonusers. The common belief that the usual mechanism of action of IUDs in women is the destruction of embryos in the uterus is not supported by empirical evidence. The bulk of the data indicate that interference with the reproductive process after fertilization has taken place is exceptional in the presence of a T-Cu or LNG-IUD and that the usual mechanism by which they prevent pregnancy in women is by preventing fertilization.The contraceptive action of all IUDs is mainly in the intrauterine cavity. Ovulation is not affected, and the IUD is not an abortifacient.58–60 It is currently believed that the mechanism of action for IUDs is the production of an intrauterine environment that is spermicidal.Nonmedicated IUDs depend for contraception on the general reaction of the uterus to a foreign body. It is believed that this reaction, a sterile inflammatory response, produces tissue injury of a minor degree but sufficient enough to be spermicidal. Very few, if any, sperm reach the ovum in the fallopian tube… In women using<unk> , sensitive assays for human chorionic gonadotropin do not find evidence of fertilization.62,63 This is consistent with the fact that the<unk> protects against both intrauterine and ectopic pregnancies.The<unk> releases free<unk>  and<unk>  salts that have both a biochemical and morphological impact on the endometrium and also produce alterations in cervical mucus and endometrial secretions... An additional spermicidal effect probably takes place in the cervical mucus.Mechanisms of actionThe common belief that the usual mechanism of action of IUDs in women is destruction of embryos in the uterus is not supported by empirical evidence... Because concern over the mechanism of action represents a barrier to acceptance of this important and highly effective method for some women and some clinicians, it is important to point out that there is no evidence to suggest that the mechanism of action of IUDs is abortifacient... the principal mechanism of action of the<unk>  T 380A IUD is to interfere with sperm action, preventing fertilization of the ovum.<unk>  acts as a spermicide within the uterus. The presence of<unk>  increases the levels of<unk>  ions, prostaglandins, and white blood cells within the uterine and tubal fluids. Although not a primary mechanism of action, some experts in human reproduction believe there is sufficient evidence to suggest that IUDs with<unk>  can disrupt implantation,Thus, both clinical and experimental evidence suggests that IUDs can prevent and disrupt implantation. It is unlikely, however, that this is the main IUD mode of action, … The best evidence indicates that in IUD users it is unusual for embryos to reach the uterus.In conclusion, IUDs may exert their contraceptive action at different levels. Potentially, they interfere with sperm function and transport within the uterus and tubes. It is difficult to determine whether fertilization of the oocyte is impaired by these compromised sperm. There is sufficient evidence to suggest that IUDs can prevent and disrupt implantation. The extent to which this interference contributes to its contraceptive action is unknown. The data are scanty and the political consequences of resolving this issue interfere with comprehensive research.p. 205:SummaryIUDs that release<unk>  or levonorgestrel are extremely effective contraceptives... Both<unk>  and levonorgestrel-releasing IUSs may interfere with implantation, although this may not be the primary mechanism of action. The devices also create barriers to sperm transport and fertilization, and sensitive assays detect hCG in less than 1% of cycles, indicating that significant prevention must occur before the stage of implantation. especially when used for emergency contraception.Other methodsAnother method of emergency contraception is the insertion of a<unk>  anytime during the preovulatory phase of the menstrual cycle and up to 5 days after ovulation. The failure rate (in a small number of studies) is very low, 0.1%.34,35 This method definitely prevents implantation, but it is not suitable for women who are not candidates for intrauterine contraception, e.g., multiple sexual partners or a rape victim. The use of a<unk> for emergency contraception is expensive, but not if it is retained as an ongoing method of contraception.Copper-releasing IUCsWhen used as a regular or emergency method of contraception,<unk> -releasing IUCs act primarily to prevent fertilization. Emergency insertion of a<unk>  IUC is significantly more effective than the use of ECPs, reducing the risk of pregnancy following unprotected intercourse by more than 99%.2,3 This very high level of effectiveness implies that emergency insertion of a<unk>  IUC must prevent some pregnancies after fertilization.Pregnancy begins with implantation according to medical authorities such as the US FDA, the National Institutes of Health79 and the American College of Obstetricians and Gynecologists (ACOG).80 Despite this, there has been no definitive evidence that IUD users have higher rates of embryonic loss than women not using contraception. Therefore, the<unk> is considered to be a true contraceptive and not an abortifacient.
Copper IUDs
Hormonal IUDs
Progestogen-only pill
Vibegron
Extended cycle combined hormonal contraceptive
Progesterone vaginal ring
High-dose estrogen
Lipoidal estradiol