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Our current freezing-thawing policy is to transfer only embryos that cleave further in the 24 h following thawing. The purpose of our study was to investigate the incidence of numerical abnormalities for chromosomes X, Y and 1 in blastomeres of human preimplantation embryos that survived cryopreservation but did not cleave further after thawing. A total of 63 embryos surviving a freezing-thawing cycle but not cleaving further within 24 h after thawing were screened. Of the 63 screened embryos that showed cleavage arrest 24 h after thawing, 56 embryos (88.9%) remained arrested 48 h after thawing and slightly more than half of these (29/56; 51.8%) showed further deterioration in morphological quality. Seven embryos (11.1%) showed signs of further cleavage; five embryos showed additional cleavage of one blastomere and two developed a blastocoelic cavity. Fluorescent in-situ hybridization (FISH) with three specific probes for simultaneous detection of chromosomes X, Y and 1 was performed and was successful in 60 out of 63 embryos. Of these successfully labelled embryos, 26 (43.3%) were in the diploid range: 12 (20%) were uniformly diploid for the chromosomes X, Y and 1; three embryos showed aneuploidy in all their blastomeres (two were XXY-karyotype and one was monosomy 1) and in 11 embryos nondisjunction was detected. Thirteen embryos were categorized as being either haploid, triploid, tetraploid or hexaploid. Nine embryos were classified as mosaic and 12 as being highly abnormal or chaotic. These preliminary results suggest that a large proportion of embryos that do not cleave further after freezing and thawing carry chromosomal aberrations. This finding supports our policy of not transferring cryopreserved embryos which do not cleave further 24 h following thawing.

Fluorescent in-situ hybridization on human embryos showing cleavage arrest after freezing and thawing