Pregnancy rates (prs) according to embryo cell number at time of embryo transfer (ET).

ABSTRACT

PURPOSE: To evaluate pregnancy and implantation rates following fresh and frozen embryo transfer (ET) according to blastomere number. METHODS: A retrospective study from 1/1/97 to 9/30/98 including all cycles with ETs irrespective of age. RESULTS: 65% of fresh transfers had at least one 8-cell embryo vs only 39.6% for frozen ET. The clinical pregnancy and implantation rates were higher when one 8-cell embryo was transferred (64% and 24%) vs a 5-7 cell embryo (41% and 14.5%) for fresh transfers. There was less of a difference with frozen ETs (46% and 19% for 8-cell vs 38% and 17% for 5-7 cell). CONCLUSIONS: Since mostly only 8-cell embryos at day 3 reach the blastocyst stage, these data raise questions as to whether the quest to attain the highest pregnancy rate per transfer through blastocyst transfer, may be at the expense of overall pregnancy rate (fresh and frozen) from a given oocyte harvest.