Higher clinical pregnancy rates from frozen-thawed blastocyst transfers compared to fresh blastocyst transfers: a retrospective matched-cohort study

The purpose of this matched-cohort study was to assess endometrial receptivity to blastocyst implantation in fresh embryo transfer by comparing implantation outcomes of fresh embryo transfer with frozen embryo transfer, where two blastocysts of good quality were transferred in good prognosis patients. Fresh embryo transfer from intracytoplasmic sperm injection cycles and artificial frozen embryo transfer cycles performed from January 2012 to December 2013 at a private clinic were retrospectively analyzed and the pregnancy, clinical pregnancy, and implantation rates statistically compared. Cycles were stratified and matched according to the blastocyst expansion grade (grade 2, 3, 4, or 5) of the two blastocysts transferred. Five hundred ninety-eight fresh embryo transfer cycles were matched with 545 frozen embryo transfer cycles across four blastocyst cohorts. In this study of 1143 blastocyst transfer cycles, fresh embryo transfer resulted in reduced pregnancy, clinical pregnancy, and fetal heart implantation rates in all four blastocyst cohorts. The fetal heart implantation rates for fresh embryo transfer ranged from 16.7 % in the grade 2 to 47.3 % in the grade 5 cohort, compared to 23.1 % in the grade 2 to 57.4 % in the grade 5 cohort for frozen embryo transfer. The trends in increasing pregnancy outcomes relative to increasing blastocyst expansion were similar in fresh embryo transfer and frozen embryo transfer. Blastocysts of good quality transferred in frozen embryo transfer had a significantly greater chance of implantation and clinical pregnancy compared to blastocysts of matched quality transferred in fresh embryo transfer, suggesting reduced endometrial receptivity in fresh embryo transfer.