EMBRYO QUALITY AND PREGNANCY POTENTIAL OF FRESH COMPARED WITH FROZEN EMBRYOS - IS FREEZING DETRIMENTAL TO HIGH-QUALITY EMBRYOS

To determine the effect of cryopreservation on embryo quality and the pregnancy potential of embryos, donated oocytes from the same donor (n = 24) were randomly allocated, with subsequent transfer to two or mor e different ovum recipients resulting in at least one fresh and one fr ozen embryo transfer cycle from the same cohort of oocytes. Endometria l receptivity was controlled in all ovum recipients, and male factor p atients were excluded. The number of embryos transferred, mean embryo grade transferred, number of high quality embryos (grade less than or equal to 2.5, grade 1 being best) transferred and embryo implantation and live birth rates are reported, Significantly more embryos (4.4 +/- 1.2 versus 3.3 +/- 1.2, P < 0.00003) of higher quality (1.9 +/- 0.5 v ersus 2.1 +/- 0.5, P < 0.013) and of a more advanced cell stage (3.0 /- 0.6 versus 2.6 +/- 0.7, P < 0.019) were transferred fresh than afte r cryopreservation respectively. Implantation rates/embryo [19/151 (12 .6%) and 9/111 (8.1%)] and live birth rates/transfer [11/42 (26.2%) an d 6/45 (13.3%)], from fresh and frozen transfers respectively, were no t significantly different despite the larger number of high quality em bryos transferred fresh. Embryo cryopreservation adversely affects emb ryo quality, but does not have detrimental effects on the implantation or pregnancy potential of high quality embryos. Because of the loss o f embryos during freeze-thawing during frozen embryo cycles, every eff ort should be made to attempt a fresh transfer.