The morphological response of blood vessels of the endometrium to low dose oral norethisterone and levonorgestrel

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Abstract
Summary The endometrial vasculature of patients taking low dose oral progestagens–norethisterone and levonorgestrel – was examined by light microscopy and electron microscopy. The endometrial spiral arteries were small and underdeveloped with a decrease in smooth muscle cells and elastic tissue in the media. Endometrial capillaries were morphologically similar to controls. Increased numbers of dilated veins were found throughout the cycle in all areas of the endometrium and predominantly under the surface epithelium. Breaks in the endothelial linings of veins with and without haemostatic plugs were increased during the intermenstrual phase of the cycle. These vascular defects are the likely morphological explanation of the bleeding complications associated with low dose oral progestagens.