The reason why women can only have intercourse after half a month of IUD placement is twofold: 1. Because the IUD surgery can cause some mechanical damage to the endometrium, the endometrium will bleed, and if intercourse causes inflammation of the endometrium, it can even affect the ability to have children. 2. The contraceptive principle of the IUD is the placement of the IUD in the uterine cavity, which can cause a sterile inflammation of the endometrium. Inflammatory cells can not only engulf sperm, and the damaged endometrium can also prevent the fertilization of the egg, thus achieving the purpose of contraception. And just after IUD, the time of IUD is short, the above mentioned effects do not occur easily, so it can lead to the failure of contraception. To sum up, women should not have intercourse within half a month after the IUD.