Clinical importance of endometrial histology and progesterone level assessment in luteal-phase defect

In order to clarify the relationship between endometrial histology and progesterone (P4), plasma P4 and estradiol levels in the luteal phase were measured in 126 cases of unexplained infertility. Endometrial biopsies were performed in the midluteal period of menstrual cycles. Forty-three of the 126 cases showed retarded endometrium. Of these 43 cases, 23 exhibited three different types of abnormal P4 secretion. Type A showed low P4 levels throughout the luteal period. Type B showed low P4 levels only in the early luteal period. Type C showed normal P4 levels in the early luteal period followed by a prompt decline. These findings indicated that P4 determination during the early, mid- and late luteal phases is necessary to assess P4 secretion. However, 20 of the 43 cases had normal P4 levels through the entire luteal phase, demonstrating an insufficient response of the endometrium to P4. Consequently, histological examination of the endometrium is required to investigate the luteal phase defect.