Analysis of information sources in references of the Wikipedia article "Hormonal intrauterine device" in English language version.
Conclusions
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 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.
Mechanisms of action
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.
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Summary
IUDs that release copper or levonorgestrel are extremely effective contraceptives... Both copper IUDs 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.
Both copper IUDs and levonorgestrel releasing IUSs may interfere with implantation
Conclusions
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 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.
Mechanisms of action
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:
Summary
IUDs that release copper or levonorgestrel are extremely effective contraceptives... Both copper IUDs 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.
Both copper IUDs and levonorgestrel releasing IUSs may interfere with implantation
Mechanism of action
Although the precise mechanism of action is not known, currently available IUCs work primarily by preventing sperm from fertilizing ova.26 IUCs are not abortifacients: they do not interrupt an implanted pregnancy.27 Pregnancy is prevented by a combination of the "foreign body effect" of the plastic or metal frame and the specific action of the medication (copper or levonorgestrel) that is released. Exposure to a foreign body causes a sterile inflammatory reaction in the intrauterine environment that is toxic to sperm and ova and impairs implantation.28,29 The production of cytotoxic peptides and activation of enzymes lead to inhibition of sperm motility, reduced sperm capacite journal and survival, and increased phagocytosis of sperm.30,31… The progestin in the LNg IUC enhances the contraceptive action of the device by thickening cervical mucus, suppressing the endometrium, and impairing sperm function. In addition, ovulation is often impaired as a result of systemic absorption of levonorgestrel.23
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Table 7-1. Myths and misconceptions about IUCs
Myth: IUCs are abortifacients. Fact: IUCs prevent fertilization and are true contraceptives.
