Donor-recipient pairs to evaluate the effect of day 3 embryos having at least six blastomeres on pregnancy outcome.

Purpose: To determine if having all embryos transferred with at least six blastomeres improves pregnancy rates compared to women having an embryo transfer with at least one embryo with less than six cells.

Methods: Donor-recipient pairs were used to help remove the confounding effect of egg quality. Four donor-recipient pair types were evaluated: (1) both donor and recipient had all embryos with at least six cells, (2) neither donor nor recipient had all embryos with > or =6 cells, (3) donor but not recipient had all > or = six cell embryos, (4) recipient but not donor had all embryos with > or = six cells. Combining donor and recipients there was a significantly higher pregnancy rate per transfer when all embryos had at least six blastomeres (50/92 or 54.3%) vs. the group with at least one embryo with <6 cells (46/121 or 38.8%). Similarly the implantation rate was significantly higher (37.8% vs. 20.3%).

Conclusions: These data corroborate conclusions made by evaluating single embryo transfer in women with diminished egg reserve that the presence of at least six blastomeres is associated with a better chance of a given embryo to implant