A morphometric study of the effect of oral norethisterone or levonorgestrel on endometrial blood vessels.

A morphometric study was undertaken to quantitate vessel numbers in uterine biopsies from a control group of patients, patients with dysfunctional uterine bleeding and patients taking low dose norethisterone or levonorgestrel. Vessels were counted at the endometrial/myometrial junction and in the functional endometrium just below the surface epithelium. The number of arteries at the endometrial/myometrial junction was found to be decreased in patients taking norethisterone and levonorgestrel. An increase was found in the total number of veins and in the number of dilated veins in the functional endometrium of the progestogen-treated specimens. Dilated veins were frequently found close to the endometrial surface and it is possible that they may be the major cause of the irregular bleeding associated with low dose oral progestogens.