The number of eight-cell embryos is a key determinant for selecting day 3 or day 5 transfer

Objective: To select patients for day 3 vs. day 5 embryo transfer. Design: Retrospective analysis of assisted reproduction technology (ART) cy cles comparing outcomes of day 3 and day 5 transfers. Setting: ART program of Brigham and Women's Hospital. Patient(s): Patients with day 3 or day 5 embryo transfers (n = 221 and 141, respectively). Intervention(s): Cycles with eight or more zygotes were stratified by the n umber of eight-cell embryos available on day 3 (none, one or two, or three or more). Main Outcome Measure(s): Number of blastocysts, implantation rates, ongoing pregnancy rates, and number of fetal heart beats. Result(s): With no eight-cell embryos on day 3, 0% and 33% pregnancies resu lted from day 5 vs. day 3 transfers. With one or two eight-cell embryos on day 3, ongoing and high order multiple rates were not different between day 3 and day 5 transfers. With three or more eight-cell embryos, day 5 transf er resulted in a decrease in multiple gestations but no difference in ongoi ng pregnancy rates compared with day 3 transfer. Conclusion(s): With no eight-cell embryos on day 3, a day 3 transfer is war ranted. With one or two eight-cell embryos, any benefit of day 5 transfer a ppears to be equivocal. With three or more eight-cell embryos, day 5 transf er is recommended. (C) 2000 by American Society for Reproductive Medicine.