GENERAL KNOWLEDGE

Detailed explanation-1: -The down-regulation of ER alpha by progesterone in the secretory phase is required for successful embryo implantation. [4] After ovulation, progesterone induces major cellular changes within the endometrium that are required to create a receptive endometrium and maintenance of early pregnancy.

Detailed explanation-2: -Progesterone and estrogen are the dominant hormonal modulators of endometrial development. Ovarian estrogen and progesterone condition the uterus for implantation, and knowledge about the precise temporal action of these hormones within the menstrual cycle has allowed the development of hormone-based contraception.

Detailed explanation-3: -This period of time where the endometrium is receptive to the embryo is called the window of implantation (WOI) and it usually occurs between days 19 and 21 of the cycle5, 6. In any other phase of the menstrual cycle, the endometrium is recalcitrant towards pregnancy7.