Changes in the pattern of cell division in the rat uterus with an intra-uterine silk thread suture in one horn were studied during the first 5 days of pregnancy.
There was no appreciable difference between the mitotic counts in the two horns on Days 1 to 4 of pregnancy, except that there was an increase in the luminal epithelial mitotic count on Day 4 of pregnancy in the horn with the device.
There was a marked difference in the luminal mitotic count between the two horns on Days 4 and 5 of pregnancy. While the mean mitotic count was 1·7 in the control horn on Day 5, it was 421 in the horn with the device. The diminution in the mitotic count seen on Day 5 of pregnancy in the control horn was not present in the horn with the device. It is possible that the effect of endogenous progesterone in causing diminished mitosis in the lumen was prevented by the presence of an IUD.