Effect of surgically induced endometriosis on pregnancy and effect of pregnancy and lactation on endometriosis in mice.

Endometriosis, a disease of women and nonhuman primates in which endometrial tissue grows outside the uterus, can be mimicked surgically in rats and mice. The disease is related to infertility in women, and surgical induction of endometriotic lesions reduces fertility in rats according to some studies. Conversely, pregnancy appears to have a beneficial effect on endometriosis in women and some rat studies. Our objective was to evaluate a new mouse model of surgically induced endometriosis with respect to the effects of pregnancy on endometriosis and the effects of endometriosis on pregnancy. Female B6C3F1 mice were divided into four groups. Those in Group A and B underwent induction surgery for endometriosis and hemi-ovariectomy, those in Group C underwent sham surgery and hemi-ovariectomy, and animals in Group D received no surgery at all. Three weeks later, Group A, C, and D were bred. Eighteen days later one half of the dams in Groups A, B, and C only were sacrificed, and evaluations included endometriotic lesion diameter, number of pups, fetal weight, and various organ weights. The remaining dams delivered, and, 18 days after parturition, dams and pups were sacrificed. Evaluations included gestation length and those listed above. Endometriotic lesion diameter was significantly reduced in pregnant animals when compared with nonpregnant controls, but the reduction was not a full regression. Lactation returned the mean lesion diameter to pre-pregnancy dimensions. When effects of endometriosis on pregnancy were evaluated, no effects on the litter size, pup weight, or gestation length were found, but trends toward increased resorptions and malformations were evident. Thus, in the mouse model of induced endometriosis, pregnancy produced a significant reduction in endometriotic lesion diameter while fertility was largely unaffected by the surgically induced endometriosis. The mouse model of endometriosis thus appears more resistant than the rat model to effects of endometriosis on fertility.