Endometrial reaction to intrauterine device in pregnancy.

It is generally assumed that the intrauterine device (IUD) exerts its action by altering endometrial receptivity for the implanting embryo. The most frequently encountered endometrial reaction reported in the presence of an IUD is a chronic inflammatory reaction which may be responsible for the alterations in the normal physiology of the human endometrium. In order to evaluate the endometrial response to the IUD when pregnancy occurs with the device in situ, we have examined the morphology of decidual tissue obtained during interruptions of pregnancy of 32 patients who had conceived in the presence of IUDs. Twenty-three decidual specimens, obtained during interruption of pregnancies without an IUD, served as controls. The incidence of chronic inflammatory reaction was 6.25% in the presence of an IUD and 4.34% in the control group. The incidence of chronic endometritis reported in nonpregnant IUD users is higher (14-100%) than the incidence of chronic endometritis observed in both groups. This observation may be the result of the generally observed alterations in the immune system during a normal pregnancy, but may also be interpreted as a primary reduced endometrial reaction to the IUD, consequently leading to the contraceptive failure in this group.