A prospective, randomized study comparing day 2 and day 3 embryo transfer in human IVF

It is believed that delayed transfer of embryos after IVF allows for a bett er selection of good quality embryos. Hence, the number of embryos and all other prognostic factors being equal, transfer of day 3 embryos should be a ssociated with higher implantation and pregnancy rates than transfer of day 2 embryos. To investigate this hypothesis, a prospective randomized study was carried out to compare implantation and pregnancy rates between day 2 a nd day 3 transfers. The relationship between the embryo quality score of da y 2 and day 3 embryos and their respective implantation rates was also anal ysed. In a 2 year period all patients undergoing infertility treatment and in whom at least seven normally fertilized oocytes were obtained were inclu ded in the study. A minimization procedure was performed taking into accoun t the patient's age and the method of fertilization (IVF or intracytoplasmi c sperm injection). By using a uniform policy of embryo transfer, the numbe r of embryos transferred was similar in both groups. The outcome parameters were embryo quality, implantation and pregnancy rates. No difference was o bserved in implantation and pregnancy rates between transfers on day 2 vers us day 3 (23.8 versus 23.8% and 47.9 versus 46.8% respectively). The incide nce of embryos of moderate to poor quality was higher in embryos cultured f or 3 days compared with those cultured for 2 days, It is concluded that the outcomes of embryo transfer in terms of implantation and pregnancy rates a re comparable for day 2 and day 3 embryos, although the overall embryo qual ity score decreases when embryos are kept in culture till day 3.