Steroid receptor expression in late follicular phase endometrium in GnRH antagonist IVF cycles is already altered, indicating initiation of early luteal phase transformation in the absence of secretory changes

Abstract

Although the current study found no early secretory transformation in stimulated endometria before hCG administration, the ER and PR expression in these endometria is similar to the one described during the first days of the luteal phase in natural cycles. Supraphysiological concentrations of estradiol and subtle progesterone rises in the late follicular phase might be responsible for this modulated steroid receptor profile. This phenomenon indicates accentuated maturation of the endometrium in IVF cycles from the pre-ovulatory phase onwards.