Her research into the potential of freeze-thawing eggs, using conventional methods of slow freezing and rapid thawing, revealed the consequences of freezing on fertilisation, subsequent initial cell division (cleavage) and embryo quality. Out of 337 thawed eggs, 263 survived (78%), 221 were fertilised using ICSI (67.9%), 116 underwent cleavage up to the second day (77.3%), 92 embryos were implanted in 37 embryo transfer procedures and two pregnancies resulted with two babies born (13.5%, although this figure was not significant due to the small numbers involved).
Dr Chamayou also found that the quality of embryos differed significantly depending on whether fresh or frozen eggs had been used; out of the total number of embryos, 36.7% were grade 1 embryos after IVF using fresh eggs, 19.5% were grade 1 after ICSI using fresh eggs (giving an overall percentage after IVF and ICSI of 24.7% grade 1 embryos), but only 12.1% were grade 1 using frozen-thawed eggs.
"We concluded that oocyte preservation decreased the proportion of cleavage and grade 1 embryos, but did not influence fertilisation rates," she said. One reason for the high percentage of failure after fertilisation could be the damage done to the structure of the egg during freeze-thawing, in particular to a part called the meiotic spindle which is involved in cell division. The meiotic spindle is a bundle of microtubules, some of which become attached to chromosomes, providing the mechanism for chromosomal movement.
"Before freezing we observed meiotic spindles in 62.5% of oocytes, but in only 43.4% after thawing. This is statistically significant and I deduced that cryopreservation may induce irreversible damage to the bonding of the microtubules," she said.'"/>