- Baseline endometrial biopsy assessed by light microscopic histological evaluation revealing: insufficient endometrial tissue for diagnosis because of insufficient available (atrophic) endometrial tissue (not because of an inaccessible cervix) and endometrial thickness < 5 mm (double layer) by transvaginal ultrasound, atrophic endometrium, secretory endometrium, menstrual type endometrium, proliferative endometrium