Ce. Selick et al., EMBRYO QUALITY AND PREGNANCY POTENTIAL OF FRESH COMPARED WITH FROZEN EMBRYOS - IS FREEZING DETRIMENTAL TO HIGH-QUALITY EMBRYOS, Human reproduction, 10(2), 1995, pp. 392-395
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.