Window of Implantation (WOI)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 7, 2026

The hormonally determined period during the secretory phase of the menstrual cycle (approximately cycle days 19 to 23 in a standard 28-day cycle) during which the endometrium is maximally receptive to embryo implantation. The WOI is precisely regulated by estrogen and progesterone and is displaced in approximately 20 to 25% of women with recurrent implantation failure, identifiable via ERA testing.²⁴²³

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.