Summary. We describe a well-established approach for studying the parameters and mechanisms of synchronization or desynchronization between the maternal and embryonic systems before implantation. It is useful for inducing 'delayed secretion' of the endometrium by different endocrine interventions, which dissociate the endometrial transformation from its control by the corpus luteum. The technique has been achieved by means of direct progesterone antagonists which competitively bind to the progesterone receptor and, in turn, inhibit the physiological effects of progesterone. During the luteal phase, secretory protein patterns indicate the receptive stage of the endometrium. Evidence is presented to show that these patterns, analysed by electro-phoresis and densitometry, define the time at which an embryo transfer is promising for implantation and establishment of pregnancy.
Keywords: uterine proteins; corpus luteum, blastocyst; implantation; progesterone antagonists; human