The endometrium in natural and artificial luteal phases

The normal human endometrium reacts precisely and sensitively to any hormonal stimulation with predictable changes. If the corpus luteum develops normally after ovulation, the progesterone secreted induces specific changes in endometrial glandular and stromal cells that can be dated by daily fine-structural alterations. With corpus luteum deficiency the endometrial differentiation is delayed and remains incomplete. The defect in the differentiation of glands and stroma varies in their distribution and intensity and may be dissociated or coordinated depending upon the cause of the corpus luteum deficiency. The administration of natural progesterone in the second half of the cycle prolongs the luteal phase and may result in hypersecretion of glands. In contrast, therapy with synthetic gestagens depresses glandular secretion, induces glandular atrophy and decidualization of the stroma. The various synthetic gestagens differ both quantitatively and qualitatively in their action; depending upon the dosage given the endometrium remains in abortive or arrested secretion. Clomiphene depresses normal secretion by its antioestrogenic effect which causes deficient oestrogen priming. On the other hand, clomiphene counteracts excessive oestrogen and will normalize the secretion in a deficient luteal phase that was preceded by follicular persistency. In the artificial cycle, depending upon the state of endogenous hormonal stimulation, the patients will benefit either from clomiphene or gonadotrophin to maintain or normalize their secretory endometrium.