Traditionally, the first day of menstruation is taken as day 1 of an idealised 28-day cycle while ovulation is conventionally timed at day 14.
Variation in the cycle is usually due to differences in the proliferative phase as collapse of the secretory phase into menstruation if fertilisation does not take place is relatively more predictable than the proliferative phase.
Because of this interplay of structure, function, and ovarian hormonal stimuli, the endometrium is considered one of the most sensitive indicators of the hypothalamic-pituitary-ovarian hormonal axis. Estradiol promotes endometrial proliferation, whereas after ovulation, progesterone converts estradiol-primed endometrium into secretory tissue.
As a result, morphologic evaluation of the endometrium is used in diagnostic evaluation of infertile patients to determine whether ovulation is occurring (Fig. Postovulatory estradiol amplifies the progesterone effect, and after withdrawal of both estradiol and progesterone, the endometrial mucosa breaks down and regenerates within the period of menstruation.
A study (2) which evaluated 1492 biopsies in 1055 women showed that diagnosis of LPD in both infertile and fertile women represents only a chance event; and hence luteal phase evaluation by histological dating of the endometrium is not worthwhile.
Moreover because of the discomfort and expense associated with endometrial biopsy, attention has turned to direct measurements of plasma progesterone levels as a means to rule out an inadequate luteal phase.
Morphologically, the endometrium is one of the most dynamic target tissues in women.
Its cyclic structural changes mirror changes in metabolic functions, and both are regulated by ovarian estradiol and progesterone. Schematic representation of steroid hormone-morphologic interactions during the endometrial cycle.
An endometrium is receptive when it is ready for the embryo implantation.
This occurs around days 19-21 in each menstrual cycle of a fertile woman..
Endometrial biopsy remains the classical way to diagnose an inadequate luteal phase.