[Effects of low doses of lynestrenol on endometrium and nidation (author's transl)]

In 10 women taking 0.5 mg lynestrenol for oral contraception endometrium biopsies were carried out in several consecutive cycles between the 21st and 25th day of each cycle. In addition pregnandiol excretion in the urine was measured in one of the last three treatment cycles always on the 10th and 21st day of cycle. During treatment of a characteristic, monomorphic microscopical endometrium picture was observed with hardly distinct endometrium glands and only slight decidualike transformation of cellular elements of the stroma. From these histological pictures it is concluded that oral application of 0,5 mg lynestrenol produces endometrium changes characterized by insufficient transformation so that nidation of a blastocyte becomes impossible.