Endometrial histomorphometry of trimegestone-based sequential hormone replacement therapy: a weighted comparison with the endometrium of the natural cycle

Histomorphometric changes in the endometrium were evaluated under the effect of a trimegestone-based sequential hormone replacement therapy (HRT) regimen, and the findings were compared to those in endometrium of the natural cycle. Endometrial samples were taken from postmenopausal women who completed a randomized, double blind, dose-ranging study of oral trimegestone (0.05, 0.1, 0.25 and 0.5 mg per day) from day 15 to day 28 with continuous micronized oestradiol 2 mg daily for six treatment cycles. The HRT-treated endometrium, irrespective of the dose, had a smaller mean total glandular area, smaller average glandular diameter, smaller mean total vascular space area and diameter than the luteal phase. Stromal cellularity was similar in the four dose groups. There were reduced glandular secretions in the endometrium from the high dose group. The relative weighting of these histological parameters was evaluated by linear discriminant analysis. The weighted values were dose independent, and may therefore represent either a specific effect of trimegestone, number of days administered, or both. We have constructed an equation to assign a value for a histological parameter which determines the position on linear discriminant functions. These assigned values can be used in other sequential HRT regimens to determine the relative influence of a given progestogen on endometrial morphology in relation to different phases of the natural cycle.