Abstract 
Background: Luteal phase support (LPS) is a crucial step in ICSI/IVF cycles for embryo implantation. It has been agreed that progesterone supplementation is an integral part of luteal phase support and implantation. Different additional supplementations have been proposed in addition to progesterone; of which estradiol was one. This study was done to compare the additive role of ostradiol supplementation to progesterone for luteal phase support compared to progesterone alone in ICSI cycles. 
Objectives: to assess the effect of oestradiol supplementation in addition to progesterone during luteal phase on the implantation rate in patients undergoing long agonist ICSI/IVF cycles.    Methods: A prospective randomized controlled double blinded study, two-hundred and thirty six patients undergoing their first ICSI cycle using the long agonist protocol, were enrolled in this study. Participants were then randomized into two equal groups of 118 patients each; Group A:  received a dose of 400 mg progesterone twice daily in the form of vaginal or rectal suppositories, in addition to (2x2) placebo oral tablets (similar to estrogen tablets). Group B:  received 400 mg progesterone twice daily in the form of vaginal or rectal suppositories, in addition to oestradiol valerate oral tablets in a dose of 4mg/day (2x2). In both groups, medications were started from the day of ovum pickup and for 14 days after embryo transfer.  Participants were further divided in to two groups, according to their oestradiol levels.  Implantation rate was set as the primary outcome, secondary outcome included chemical, clinical pregnancy and miscarriage rate per cycle. Results: The implantation rate was significantly higher in the progesterone only group (Group A) compared to oestradiol and progesterone group (GroupB) (12.88% vs 7.98% respectively) 
Conclusion: Supplementation of oestradiol to progesterone in luteal phase support confers no additional benefit to progesterone alone. 
Further studies are required to elucidate the role of oestradiol in the luteal phase support in ICSI cycles.