(1) As an alien foreign body, the IUD occupies a certain space in the uterine cavity, so that the fertilized egg can't be implanted and can't survive and develop.
(2) The sterilizer stimulates the endometrium and causes a mild aseptic inflammatory reaction. A large number of leukocytes and phagocytes are produced, which have a toxic effect on the embryo. At the same time phagocytes can also engulf sperm and even dissolve fertilized eggs, thus achieving the purpose of contraception.
(3) The birth control device stimulates the endometrium to produce prostaglandins for a long period of time, causing the uterus to contract and prompting the fallopian tube to hyperperistalsis, so that the fertilized egg enters the uterine cavity in advance, so that the development of the fertilized egg and the endometrium is out of sync, thus affecting the fertilized egg implantation.
(4) The slow release of copper ions from the copper IUD changes the environment of the uterine cavity, interfering with the metabolism of the endometrial cells and affecting the egg's implantation, thus playing a contraceptive role. Most of the copper ions are absorbed by the endometrium and discharged with menstruation, which does not affect the level of copper ions in the systemic blood and does not cause copper poisoning.
(5) The IUD with progesterone can slowly release progesterone for a long time, making the endometrial glands atrophy and the interstitial metaplasia, which is not conducive to the implantation of the pregnant egg. In addition, progesterone makes the cervical mucus become sticky, preventing sperm from passing through and preventing the egg from being fertilized.