Exogenous gonadotropins--serum oestrogen and progesterone and the effect on endometrial morphology in the rat.

The serum levels of oestrogen and progesterone in hyperstimulated, pregnant rats were compared with those of normal pregnant animals. The endometrial morphology was studied before (4.5 days), at the time of (5.5 days) and after (6.5 days) implantation. In the hyperstimulated group serum oestradiol levels were significantly higher than in the controls at 2.5 and 4.5 days, while progesterone levels were similar in the two groups. Consequently the progesterone:oestradiol ratio was significantly lower in the experimental groups prior to implantation. Significant changes in the endometrium caused by the raised oestradiol levels, included an early increase in gland epithelial height, increased surface epithelial height, increased number and length of microvilli, deficiencies in the glycocalyx and decreased mitotic activity in the surface epithelium and stromal cells. In addition, epithelial cell degeneration and failure of decidualisation of stromal cells was observed. These morphological changes adversely affect embryo attachment and implantation. Similar pathological changes in the endometrium may occur in human in vitro fertilisation utilising superovulation and may be an important factor in the low success rate of these programmes.