There will be general interest in experiments described by Dr L Thomson and others in their paper using one of our Kryo 10 controlled rate freezers. The paper (published in Fertility and Sterility) looks at cryopreservation of human spermatozoa in liquid nitrogen - an established routine in ART - first introduced in the 1960s. Past studies have reported on the motility, vitality, and morphology of human spermatozoa following repeated cycles of freezing and thawing. There is an overall agreement that the percentages of both motile and viable sperm decrease steadily following each freeze–thaw cycle but the number of successful cycles possible differs between studies. This Sydney study examined the DNA integrity of the spermatozoa of infertility patients, known to have an increased susceptibility to cryo-injury, following repeated freezing and thawing. It is common practice in ART laboratories to offer at least one repeated freezing cycle to patients to maximize the use of donor or partner sperm for various reasons - for example patients who bank semen before commencing treatment for cancer regularly request refreezing of sperm when they have a limited supply.

Retaining DNA integrity is of great concern, as increased sperm DNA fragmentation has been shown to reduce the full-term pregnancy rate in ART as well as increase the risk of miscarriage so the aim of the study was to determine whether the effects of subsequent cycles of cryopreservation and thawing of spermatozoa from men presenting for infertility investigations had any cumulative effects on induced DNA damage; also whether this practice presented a level of risk comparable to that of a single cycle of cryopreservation and thawing. The study confirmed the assumption that the process of cryopreservation of spermatozoa did generate and exacerbate the level of DNA fragmentation in human spermatozoa. It however also demonstrated for the first time that up to three cycles of freezing and thawing can be performed with a level of risk to sperm DNA comparable to that following a single cycle of freezing and thawing; this, provided that samples were refrozen in their original cryoprotectant and not washed or altered in any way. The authors conclude with the practical suggestion that a small aliquot of the thawed semen is removed and prepared for insemination and the remainder immediately reloaded into semen straws or vials and refrozen.

Thomson, L., Fleming, S., Barone, K., Zieschang, J. and Clark, A. (2010),
'The effect of repeated freezing and thawing on human sperm DNA fragmentation', Fertility and Sterility, vol 93, no 4 , pp 1147 - 1156.

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