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STUDY QUESTION What technique can be used to successfully cryopreserve three or fewer ejaculated spermatozoa from cryptozoospermic men and is the physical and cognitive development of children born after this technique normal? SUMMARY ANSWER The modified cryopreservation method for three or fewer human spermatozoa from cryptozoospermic men showed a recovery rate above 95% and a survival rate just under 90%, and the physical and cognitive abilities of the children born after ICSI were comparable to those born after natural conception. WHAT IS KNOWN ALREADY Clinical outcomes of ICSI using cryptozoospermic men’s ejaculated spermatozoa are considered to be inferior to that using testicular spermatozoa from microsurgical testicular sperm extraction (Micro-TESE), possibly because the DNA fragmentation rate is higher in ejaculated spermatozoa than in testicular spermatozoa from Micro-TESE. STUDY DESIGN, SIZE, DURATION Evaluation of the efficiency of cryopreservation of three or fewer spermatozoa was conducted retrospectively at St. Mother Clinic. The physical and cognitive development of children born after this method was studied between 2011 and 2018. PARTICIPANTS/MATERIALS, SETTING, METHODS This study included 28 cryptozoospermic men who had three or fewer morphologically normal and motile spermatozoa in their ejaculate after centrifugation and who preferred using cryopreserved spermatozoa to Micro-TESE. Control subjects were 31 cryptozoospermic patients using fresh spermatozoa from their ejaculates and 20 non-obstructive azoospermic patients with fewer than 10 spermatozoa obtained by TESE and vitrified. Clinical outcomes among three groups, vitrified spermatozoa from the ejaculate, fresh spermatozoa from the ejaculate and vitrified spermatozoa from the testis, were statistically analysed. For the 7-year follow up study of the 14 children born after ICSI using the ejaculated vitrified spermatozoa, the Japanese government-issued Boshi Kenko Techo (Mother-Child Handbook) and Kinder Infant Development Scale (KIDS scale) were used to determine whether their physical and cognitive development was comparable to that of naturally conceived children. MAIN RESULTS AND THE ROLE OF CHANCE Recovery and survival rates were 97.8% (510/521) and 87.1% (444/510) for vitrified spermatozoa from the ejaculate and 92.7% (152/164) and 60.5% (92/152) for vitrified spermatozoa from the testis. Clinical pregnancies (%), miscarriages (%) and live birth rates (%), respectively, among the three groups were as follows: vitrified spermatozoa from the ejaculate: 15(25.0), 2(13.3), 13(21.7); fresh spermatozoa from the ejaculate: 26(24.3), 5(19.2), 20(18.7); and vitrified spermatozoa from the testis: 3(16.7), 0(0.0), 3(16.7). Among the groups, there were no statistically significant differences except for the sperm survival rate and the oocyte fertilisation rate, which were lower for vitrified spermatozoa from the testis compared with vitrified spermatozoa from the ejaculate. The 7-year follow-up study showed that the physical and cognitive development of 14 children born after ICSI using vitrified ejaculated spermatozoa from the ejaculate was comparable to that of naturally conceived children. LIMITATIONS, REASONS FOR CAUTIONS The maximum number of spermatozoa to which this method can be applied successfully is about 10. When the number of aspirated spermatozoa is over 10, some of them change direction after colliding with each other inside the aspiration pipette and reach the mineral oil, and once this happens, they cannot be expelled out of the pipette. Even though we did not find evidence of DNA fragmentation, further studies with larger participant numbers and longer time periods are necessary. WIDER IMPLICATIONS OF THE FINDINGS This technique is very useful for the cryopreservation of very small numbers of testicular spermatozoa (fewer than 10) in order to avoid or reduce Micro-TESE interventions. STUDY FUNDING/COMPETING INTEREST(S) No external funding was received to undertake this study. There are no competing interests. TRIAL REGISTRATION NUMBER

human reproduction

Modified permeable cryoprotectant-free vitrification method for three or fewer ejaculated spermatozoa from cryptozoospermic men and 7-year follow-up study of 14 children born from this method