Abstract
Histological “dating” of endometrial biopsy specimens within the postovulatory period was performed in a group of normal women having an I.U.D. and another group of normal women without an I.U.D. In both groups the time of ovulation was determined by basal temperature measurement. By comparing the “histological” date with the actual point of time in the cycle, given in days after the ovulation, the group of women with an I.U.D. showed an average retardation of 2 days. In the control group the average retardation was zero days. The difference between the two groups was statistically significant. The group with an I.U.D. presented focal stromal changes, which should be investigated further with a view to a possible endocrine secretion. The results of the present investigation of a fairly small series show that the contraceptive effect of an I.U.D. may be due to delayed endometrial development.