What is the Origin of Window of Implantation?

The concept is rooted in classical reproductive physiology, recognizing that endometrial receptivity is not continuous but a transient, tightly regulated biological event. In a typical 28-day cycle, this window classically opens around day 19 and lasts approximately four days.

What is the Mechanism of Window of Implantation?

The opening and closing of the WOI are entirely dependent upon the precise, sequential signaling of ovarian steroid hormones. Following ovulation, the dramatic surge and sustained presence of progesterone, acting on an estrogen-primed endometrium, triggers a cascade of molecular and structural changes, including the expression of specific adhesion molecules and growth factors, that render the uterine lining receptive to the blastocyst.

Window of Implantation ∞ Area

Window of Implantation

Meaning

The Window of Implantation (WOI) is a finite and critically timed period during the mid-luteal phase of the menstrual cycle when the uterine endometrium is physiologically receptive to an embryo, permitting successful attachment and subsequent pregnancy. This phase represents the moment of optimal synchronization between the developing embryo and the maternal uterine lining. Its precise timing is paramount for both natural conception and assisted reproductive technologies.