A total of 364 consecutive patients requesting in-vitro fertilization
(IVF) treatment were divided randomly into two groups, In the first gr
oup, two embryos in the original NF cycle were allowed to divide prior
to transfer with any remaining embryos bring cryopreserved at the pro
nucleate (PN) stage, In the second group, all the embryos were allowed
to divide to the early cleavage (EC) stage, and the best two replaced
; any suitable remaining embryos were frozen at the 2- to 4-cell stage
, A total of 134 cycles (36.8%) fulfilled the study criteria for a fre
sh embryo replacement and supernumerary embryos cryopreserved. In the
PN group, 72 out of 182 (39.6%) patients had a fresh embryo replacemen
t accompanied by embryo cryopreservation, which was not significantly
different from the EC group (62/182; 34.1%), The livebirth rate per fr
esh embryo transfer in the EC group (17/62; 27.4%) was significantly h
igher than that for the PN group (8/72; 11.1%; P < 0.05). Embryo survi
val following thawing was similar for the PN (96/129; 74.4%) and EC (7
9/102; 77.4%) stages, Although not significant, the livebirth rate fol
lowing the transfer of thawed embryos was higher in the PN group (11/4
4; 25.0%) than in the EC group (4/38; 10.5%). Following one fresh and
two freeze-thaw embryo replacements, the observed cumulative viable pr
egnancy rates were comparable for patients in both the PN (40.2%) and
EC (41.1%) groups.