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Liang MY, Lin M, Qin X, Yang R, Hu KL, Li R. Long-term embryo vitrification is associated with reduced success rates in women undergoing frozen embryo transfer following a failed fresh cycle. Eur J Obstet Gynecol Reprod Biol 2024; 296:244-249. [PMID: 38484616 DOI: 10.1016/j.ejogrb.2024.03.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Revised: 01/08/2024] [Accepted: 03/02/2024] [Indexed: 04/19/2024]
Abstract
OBJECTIVE To investigate the association of long-term embryo vitrification with the success rates and neonatal outcomes in frozen cycles. STUDY DESIGN A single-center, retrospective cohort study was performed in Peking University Third Hospital. We included women who had undergone their first vitrified-warmed cycles following an unsuccessful fresh embryo transfer cycle between January 2013 and December 2019. Restricted cubic splines with 4 knots (at min-3.0 months, 3.1-6.0 months, 6.1-12.0 months, 12.1-max months) were used to map the non-linear relationship between live birth and embryo storage time as a continuous variable after adjustment for covariates. Multiple logistic regression was used to calculate crude odds ratios (OR) and adjusted OR (aOR) with 95 % confidence intervals (CI). RESULTS A total of 10,167 women undergoing their first frozen cycle following an unsuccessful fresh embryo transfer cycle were included, among whom 3,708 resulted in a live birth (3,254 singleton live births). Restricted cubic splines, both before and after adjusting for covariates, showed that the predicted live birth rate (LBR) progressively decreased with an increase in the duration of embryo cryopreservation. This trend was also evident when women were categorized into four groups based on the length of cryopreservation. The live birth rate (LBR) was highest in the 0.8-3.0 months group (38 %) compared to the other groups. Multivariable logistic regression with the 0.8-3.0 months group as the reference, demonstrated that the 6.1-12.0 months group and >12.0 months group experienced lower live birth rates (aOR = 0.82 (0.72, 0.94) and aOR = 0.71 (0.57, 0.88), respectively). The LBR for the 3.1-6.0 months group was comparable to that of the 0.8-3.0 months group, with an aOR of 0.98 (0.90, 1.07). Sensitivity analyses in women who underwent single blastocyst transfer, in women with at least one good-quality embryo for transfer, and in women with age less than 36 at embryo transfer demonstrated a similar association between LBR and embryo frozen time. The neonatal outcomes were not significantly different among the four groups. CONCLUSIONS Embryo vitrification greater than six months is associated with a reduction in success rate but does not appear to alter neonatal outcome.
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Affiliation(s)
- Ming-Yu Liang
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, 100191 Beijing, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), 100191 Beijing, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, 100191 Beijing, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, 100191 Beijing, China
| | - Mingmei Lin
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, 100191 Beijing, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), 100191 Beijing, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, 100191 Beijing, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, 100191 Beijing, China
| | - Xunsi Qin
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, 100191 Beijing, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), 100191 Beijing, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, 100191 Beijing, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, 100191 Beijing, China
| | - Rui Yang
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, 100191 Beijing, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), 100191 Beijing, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, 100191 Beijing, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, 100191 Beijing, China
| | - Kai-Lun Hu
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, 100191 Beijing, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), 100191 Beijing, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, 100191 Beijing, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, 100191 Beijing, China.
| | - Rong Li
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, 100191 Beijing, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), 100191 Beijing, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, 100191 Beijing, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, 100191 Beijing, China.
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Zheng Q, Mo M, Zhang H, Xu S, Xu F, Wang S, Zeng Y. Prolong cryopreservation duration negatively affects pregnancy outcomes of vitrified-warmed blastocyst transfers using an open-device system: A retrospective cohort study. Eur J Obstet Gynecol Reprod Biol 2023; 281:68-75. [PMID: 36566684 DOI: 10.1016/j.ejogrb.2022.12.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2022] [Revised: 11/20/2022] [Accepted: 12/05/2022] [Indexed: 12/12/2022]
Abstract
OBJECTIVE To investigate the impact of cryopreservation (CP) duration on pregnancy outcomes of vitrified-warmed blastocysts transfers using an open-device liquid-nitrogen (LN2) system. METHODS This retrospective cohort study was conducted on 6327 first vitrified-warmed single blastocyst transfer cycles with autologous oocytes from January 2015 to December 2020. The CP duration was initially divided into six groups: Group I: 0-3 months (n = 4309); Group II: 4-6 months (n = 1061); Group III: 7-12 months (n = 304); Group IV: 13-24 months (n = 113); Group V: 25-72 months (n = 466); Group VI: 73-120 months (n = 74). Multivariate logistic regression was performed to evaluate the independent effect of CP duration on pregnancy outcomes. To further examine the time limit of vitrification, propensity score matching (PSM) was applied to compare pregnancy outcome of patients with storage duration of 25-120 months to those of 0-24 months. After that, pregnancy outcomes were compared among the subgroups of Group I': 0-24 months, Group II': 25-48 months, Group III': 49-72 months, Group IV': 73-120 months. Stratification analysis based on embryo quality was also performed. Primary outcomes were clinical pregnancy rate and live birth rate. Secondary outcomes were implantation, biochemical pregnancy rate, ongoing pregnancy rate and early miscarriage rate. RESULTS Logistic regression demonstrated that the odds of pregnancy outcomes were similar across Group I to IV. However, the implantation rate, chances of biochemical pregnancy, clinical pregnancy, ongoing pregnancy, and live birth significantly decreased as the storage duration increased up to 25 months, while miscarriage rate did not significantly differ between groups. Subgroup analysis confirmed a dramatical decrease of clinical pregnancy and live birth rate when cryopreserved for more than 24 months. After that, the slope was relatively steady between 25 and 72 months, then steeply decreased again as CP reached 73-120 months. In addition, there was a more remarkable decline of pregnancy outcomes in the average quality embryo transfers than in the high quality embryo transfers as cryopreservation storage increased. CONCLUSION Prolonged cryopreservation of vitrified blastocysts in an open-device LN2 system up to 24 months might negatively affect pregnancy outcomes. This negative impact progresses as storage duration increases, especially when exceeds 72 months. Average quality embryo appears to be less sustainable with long-term cryo-storage.
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Affiliation(s)
- Qizhen Zheng
- Shenzhen Key Laboratory of Reproductive Immunology for Peri-Implantation, Shenzhen Zhongshan Institute for Reproduction and Genetics, Fertility Center, Shenzhen Zhongshan Urology Hospital, Shenzhen 518045, Guangdong, People's Republic of China
| | - Meilan Mo
- Shenzhen Key Laboratory of Reproductive Immunology for Peri-Implantation, Shenzhen Zhongshan Institute for Reproduction and Genetics, Fertility Center, Shenzhen Zhongshan Urology Hospital, Shenzhen 518045, Guangdong, People's Republic of China
| | - Hongzhan Zhang
- Shenzhen Key Laboratory of Reproductive Immunology for Peri-Implantation, Shenzhen Zhongshan Institute for Reproduction and Genetics, Fertility Center, Shenzhen Zhongshan Urology Hospital, Shenzhen 518045, Guangdong, People's Republic of China
| | - Shiru Xu
- Shenzhen Key Laboratory of Reproductive Immunology for Peri-Implantation, Shenzhen Zhongshan Institute for Reproduction and Genetics, Fertility Center, Shenzhen Zhongshan Urology Hospital, Shenzhen 518045, Guangdong, People's Republic of China
| | - Fen Xu
- Shenzhen Key Laboratory of Reproductive Immunology for Peri-Implantation, Shenzhen Zhongshan Institute for Reproduction and Genetics, Fertility Center, Shenzhen Zhongshan Urology Hospital, Shenzhen 518045, Guangdong, People's Republic of China
| | - Sisi Wang
- Shenzhen Key Laboratory of Reproductive Immunology for Peri-Implantation, Shenzhen Zhongshan Institute for Reproduction and Genetics, Fertility Center, Shenzhen Zhongshan Urology Hospital, Shenzhen 518045, Guangdong, People's Republic of China
| | - Yong Zeng
- Shenzhen Key Laboratory of Reproductive Immunology for Peri-Implantation, Shenzhen Zhongshan Institute for Reproduction and Genetics, Fertility Center, Shenzhen Zhongshan Urology Hospital, Shenzhen 518045, Guangdong, People's Republic of China.
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Li X, Guo P, Blockeel C, Li X, Deng L, Yang J, Li C, Lin M, Wu H, Cai G, Hu Y, Chen X. Storage duration of vitrified embryos does not affect pregnancy and neonatal outcomes after frozen-thawed embryo transfer. Front Endocrinol (Lausanne) 2023; 14:1148411. [PMID: 36998477 PMCID: PMC10043480 DOI: 10.3389/fendo.2023.1148411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Accepted: 02/28/2023] [Indexed: 03/18/2023] Open
Abstract
BACKGROUND With the refinement of cryopreservation technology, the number of frozen-warmed embryo transfer (FET) cycles and cryopreserved embryos has increased rapidly. However, studies investigating the effect of storage duration on pregnancy outcomes after vitrification are limited and their results are controversial. Furthermore, the available studies did not take patients' demographic nor clinical treatment characteristics into account and the cryo-storage duration was short. So this study aimed to explore the effect of storage duration of vitrified warmed embryos on pregnancy and neonatal outcomes in patients with good prognosis and long storage duration of vitrified embryos. METHODS This study was a bi-centre, retrospective study including 1037 women undergoing their first FET cycles following a fresh cycle from January 2012 until December 2021. Patients were divided into four storage groups in accordance with the storage duration of transferred embryos (612 patients in group I, with storage duration between 1 and 6 months; 202 patients in group II, with storage duration between 7 and 12 months; 141 patients in group III, with storage duration between 13 and 36 months; and 76 patients in group IV, with storage duration between 37 and 84 months). The pregnancy and neonatal outcomes were compared amongst different storage duration groups. RESULTS Amongst the different groups, no significant differences were observed in the pregnancy outcomes, including biochemical pregnancy rate, implantation rate, clinical pregnancy rate, ongoing pregnancy rate and live birth rate. In addition, no evidence of differences amongst different storage duration groups was observed in terms of preterm birth, birth length and low birthweight. CONCLUSIONS The pregnancy and neonatal outcomes of embryos after vitrification were not impaired by storage duration up to 7 years.
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Affiliation(s)
- Xuelan Li
- Reproductive Medicine Center, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
| | - Pingping Guo
- Reproductive Medicine Center, Zhuhai Maternal and Childcare Service Center, Zhuhai, Guangdong, China
| | - Christophe Blockeel
- Centre for Reproductive Medicine, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium
| | - Xinning Li
- Reproductive Medicine Center, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
| | - Ling Deng
- Reproductive Medicine Center, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
| | - Jie Yang
- Reproductive Medicine Center, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
| | - Chujun Li
- Reproductive Medicine Center, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
| | - Min Lin
- Reproductive Medicine Center, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
| | - Haocun Wu
- Department of Clinical Laboratory, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
| | - Guifeng Cai
- Reproductive Medicine Center, Zhuhai Maternal and Childcare Service Center, Zhuhai, Guangdong, China
- *Correspondence: Xin Chen, ; Yunzhao Hu, ; Guifeng Cai,
| | - Yunzhao Hu
- Reproductive Medicine Center, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
- *Correspondence: Xin Chen, ; Yunzhao Hu, ; Guifeng Cai,
| | - Xin Chen
- Reproductive Medicine Center, Shunde Hospital of Southern Medical University (The First People’s Hospital of Shunde), Foshan, Guangdong, China
- *Correspondence: Xin Chen, ; Yunzhao Hu, ; Guifeng Cai,
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Hu KL, Hunt S, Zhang D, Li R, Mol BW. The association between embryo storage time and treatment success in women undergoing freeze-all embryo transfer. Fertil Steril 2022; 118:513-521. [PMID: 35934542 DOI: 10.1016/j.fertnstert.2022.06.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 05/11/2022] [Accepted: 06/03/2022] [Indexed: 01/13/2023]
Abstract
OBJECTIVE To investigate the relationship between the embryo frozen time and live birth rate (LBR) in women having a freeze-all cycle. DESIGN Retrospective cohort study. SETTING Academic hospital. PATIENT(S) Women who underwent their first vitrified-warmed cycles from January 2013 to December 2019. INTERVENTION(S) Embryo storage time. MAIN OUTCOME MEASURE(S) The primary outcome was the LBR. RESULT(S) A total of 14,928 women were eligible for the analysis. Women with the frozen time of transferred embryos for 2-5 months were associated with a higher LBR compared with other groups. The results were confirmed by an inverted U curve in the restricted cubic splines before as well as after adjustment for covariables, which suggested that an embryo storage time of 3-4 months was associated with the highest LBR. Subgroup analyses demonstrated that the inverted U curve relationship between embryo storage time and LBR was only observed in women with the high response. Sensitivity analyses in women with at least one good-quality embryo for transfer, in women aged <36 years at embryo transfer, or in women with double cleavage embryo transfer showed that the association remained valid. The association was weakened in women with single blastocyst transfer probably because of the small sample size in these women. CONCLUSION(S) An inverted U-shaped relationship was found between embryo storage time and treatment success in women with high ovarian response in freeze-all embryo transfer cycles. Prolonged storage time of >6 months was associated with reduced pregnancy rates.
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Affiliation(s)
- Kai-Lun Hu
- Center for Reproductive Medicine, Peking University Third Hospital, Haidian District, Beijing, the People's Republic of China; Key Laboratory of Reproductive Genetics (Ministry of Education) and Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, the People's Republic of China
| | - Sarah Hunt
- Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
| | - Dan Zhang
- Key Laboratory of Reproductive Genetics (Ministry of Education) and Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, the People's Republic of China
| | - Rong Li
- Center for Reproductive Medicine, Peking University Third Hospital, Haidian District, Beijing, the People's Republic of China.
| | - Ben W Mol
- Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia
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Logsdon DM, Grimm CK, Schoolcraft WB, McCormick S, Schlenker T, Swain JE, Krisher RL, Yuan Y, Collins MG. Evaluation of the TMRW vapor phase cryostorage platform using reproductive specimens and in vitro extended human embryo culture. F&S SCIENCE 2022; 2:268-277. [PMID: 35560277 DOI: 10.1016/j.xfss.2021.06.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 06/28/2021] [Accepted: 06/30/2021] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To assess the impact of shipment and storage of sperm, oocytes, and blastocysts in vapor phase nitrogen compared with static storage in liquid phase nitrogen. DESIGN Prospective cohort-matched study. SETTING Multiple in vitro fertilization laboratories in an in vitro fertilization network. PATIENT(S) Fifty-eight human embryos, 32 human oocytes, 15 units of bovine semen. INTERVENTION(S) Vapor vs. liquid nitrogen. MAIN OUTCOME MEASURE(S) The postwarming survival of oocytes, sperm, and blastocysts, and the developmental potential of blastocysts during in vitro extended culture. RESULT(S) Custom-designed labware, for use with the TMRW platform, enables continuous temperature monitoring during shipment and/or storage in the vapor phase robotic storage system. The highest temperature recorded for specimens shipped to a domestic laboratory was -180.2 °C with a mean ± SD of -190.4 ± 0.5 °C during shipment and -181.1 ± 0.6 °C during storage. Likewise, specimens shipped internationally had a high of -180.2 °C with a mean ± SD of -193.5 ± 0.6 °C during shipment and -181.2 ± 0.7 °C during storage. Results from the extended culture assays have revealed no deleterious effect of shipment and storage in nitrogen vapor. The viability of mammalian gametes and embryos was equivalent between the vapor phase and liquid phase storage. CONCLUSION(S) The evaluated system did not have any deleterious effects on the postwarming survival of sperm, oocytes, and blastocysts. The postwarming developmental potential of human blastocysts during in vitro extended culture was unaffected by storage and handling in the vapor phase nitrogen TMRW platform when compared with static liquid phase nitrogen storage. Our results suggest that the vapor phase cryostorage platform is a safe system to handle and store reproductive specimens for human assisted reproductive technology.
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Affiliation(s)
- Deirdre M Logsdon
- Colorado Center for Reproductive Medicine-Colorado, Lone Tree, Colorado
| | - Courtney K Grimm
- Colorado Center for Reproductive Medicine-Colorado, Lone Tree, Colorado
| | | | - Sue McCormick
- Colorado Center for Reproductive Medicine-Colorado, Lone Tree, Colorado
| | - Terry Schlenker
- Colorado Center for Reproductive Medicine-Colorado, Lone Tree, Colorado
| | - Jason E Swain
- Colorado Center for Reproductive Medicine Fertility Network, Lone Tree, Colorado
| | - Rebecca L Krisher
- Colorado Center for Reproductive Medicine-Colorado, Lone Tree, Colorado
| | - Ye Yuan
- Colorado Center for Reproductive Medicine-Colorado, Lone Tree, Colorado
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Li J, Yin M, Wang B, Lin J, Chen Q, Wang N, Lyu Q, Wang Y, Kuang Y, Zhu Q. The effect of storage time after vitrification on pregnancy and neonatal outcomes among 24 698 patients following the first embryo transfer cycles. Hum Reprod 2021; 35:1675-1684. [PMID: 32575120 DOI: 10.1093/humrep/deaa136] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2019] [Revised: 04/08/2020] [Indexed: 11/14/2022] Open
Abstract
STUDY QUESTION To evaluate the impact of storage time after vitrification on embryo viability, pregnancy outcomes and neonatal outcomes. SUMMARY ANSWER The prolonged storage time of vitrified embryos negatively affected pregnancy outcomes, including biochemical pregnancy rate, clinical pregnancy and live birth rate; but did not influence neonatal outcomes. WHAT IS KNOWN ALREADY Although vitrification has been the fundamental tool of ART treatments in recent years, few studies have explored the influence of storage period after vitrification on embryonic and clinical outcomes. STUDY DESIGN, SIZE, DURATION A retrospective study was performed among 24 698 patients with the first vitrified embryo transfer following a freeze-all strategy during the period from January 2011 to December 2017. PARTICIPANTS/MATERIAL, SETTING, METHODS A total of 24 698 patients met the inclusion criteria and were grouped according to the storage time (11 330 patients in Group 1 with storage time <3 months, 9614 patients in Group 2 with storage time between 3 and 6 months, 3188 patients in Group 3 with storage time between 6 and 12 months and 566 in Group 4 with storage time between 12 and 24 months). The pregnancy outcomes and neonatal outcomes were compared between different storage time groups. Multivariate logistic regression and linear regression were performed to evaluate the independent effect of storage time on clinical outcomes, adjusting for important confounders. MAIN RESULTS AND THE ROLE OF CHANCE After adjustment for potential confounding factors, the chance of biochemical pregnancy (Group 1 as reference; Group 2: adjusted odds ratio (aOR) = 0.92, 95% CI 0.87-0.97; Group 3: aOR = 0.83, 95% CI 0.76-0.90; Group 4: aOR = 0.68, 95% CI 0.56-0.81), clinical pregnancy (Group 2: aOR = 0.91, 95% CI 0.86-0.96; Group 3: aOR = 0.80, 95% CI 0.73-0.87; Group 4: aOR = 0.65, 95% CI 0.54-0.79) and live birth (Group 2: aOR = 0.89, 95% CI 0.85-0.95; Group 3: aOR = 0.83, 95% CI 0.76-0.91; Group 4: aOR = 0.59, 95% CI 0.48-0.72) significantly decreased with the increasing storage time, whereas the relationship between miscarriage, ectopic pregnancy and storage time did not reach statistical significance. In addition, there was no evidence of differences in adverse neonatal outcomes (preterm birth, low birthweight, high birthweight, macrosomia or birth defects) between groups. LIMITATION, REASONS FOR CAUTION Our study was limited by the retrospective design from a single center, the conclusion from our study needs to be verified in further studies. WIDER IMPLICATIONS OF THE FINDINGS This study provides new findings about the relationship between prolonged storage time of vitrified embryos and clinical outcomes and offers evidence for the safety of using long-stored embryos after vitrification. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the National Natural Science Foundation of China (grant nos. 81903324, 81771533, 81571397, 81701523), National Key Research and Development Program of China (grant no. SQ2018YFC100163). None of the authors have any conflicts of interest to declare.
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Affiliation(s)
- Jianghui Li
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Mingru Yin
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Bian Wang
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Jiaying Lin
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Qiuju Chen
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Ningling Wang
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Qifeng Lyu
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Yun Wang
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Yanping Kuang
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
| | - Qianqian Zhu
- Department of Assisted Reproduction, Shanghai Ninth people's hospital affiliated to JiaoTong University School of Medicine, Shanghai, China
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Sekhon L, Lee JA, Flisser E, Copperman AB, Stein D. Blastocyst vitrification, cryostorage and warming does not affect live birth rate, infant birth weight or timing of delivery. Reprod Biomed Online 2018; 37:33-42. [DOI: 10.1016/j.rbmo.2018.03.023] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 03/26/2018] [Accepted: 03/27/2018] [Indexed: 01/28/2023]
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Anav M, Ferrières-Hoa A, Gala A, Fournier A, Zaragoza S, Vintejoux E, Vincens C, Hamamah S. [Birth weight and frozen embryo transfer: State of the art]. ACTA ACUST UNITED AC 2018; 46:489-496. [PMID: 29680508 DOI: 10.1016/j.gofs.2018.03.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Indexed: 11/26/2022]
Abstract
The aim of this study was to update our acknowledgment if there is a link between assisted embryo cryopreservation and epigenetics in human? Animal studies have demonstrated epigenetics consequence and especially imprinting disorders due to in vitro culture. In human, it is important to note that after frozen embryo transfer birth weight is significantly increased by 81 to 250g. But these studies cannot identify the reasons of such difference. This review strongly suggests that embryo cryopreservation is responsible for birth weight variations but mechanisms not yet elucidated. Epigenetics is probably one of these but to date, none study is able to prove it. We have to be attentive on a possible link between assisted reproductive technology (ART) and epigenetics reprogrammation.
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Affiliation(s)
- M Anav
- Département biologie de la reproduction/DPI, hôpital Arnaud-de-Villeneuve, 371, avenue du Doyen-Gaston-Giraud, 34295, Montpellier, France
| | - A Ferrières-Hoa
- Département biologie de la reproduction/DPI, hôpital Arnaud-de-Villeneuve, 371, avenue du Doyen-Gaston-Giraud, 34295, Montpellier, France
| | - A Gala
- Département biologie de la reproduction/DPI, hôpital Arnaud-de-Villeneuve, 371, avenue du Doyen-Gaston-Giraud, 34295, Montpellier, France
| | - A Fournier
- Département biologie de la reproduction/DPI, hôpital Arnaud-de-Villeneuve, 371, avenue du Doyen-Gaston-Giraud, 34295, Montpellier, France
| | - S Zaragoza
- Département biologie de la reproduction/DPI, hôpital Arnaud-de-Villeneuve, 371, avenue du Doyen-Gaston-Giraud, 34295, Montpellier, France
| | - E Vintejoux
- Service de gynécologie obstétrique, CHU Arnaud-de-Villeneuve, 371, avenue du Doyen-Gaston-Giraud, 34295, Montpellier, France
| | - C Vincens
- Service de gynécologie obstétrique, CHU Arnaud-de-Villeneuve, 371, avenue du Doyen-Gaston-Giraud, 34295, Montpellier, France
| | - S Hamamah
- Département biologie de la reproduction/DPI, hôpital Arnaud-de-Villeneuve, 371, avenue du Doyen-Gaston-Giraud, 34295, Montpellier, France.
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Kim HJ, Park SB, Yang JB, Choi YB, Lee KH. Effects of laser-assisted hatching and exposure time to vitrification solution on mouse embryo development. Clin Exp Reprod Med 2018; 44:193-200. [PMID: 29376016 PMCID: PMC5783916 DOI: 10.5653/cerm.2017.44.4.193] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Revised: 09/03/2017] [Accepted: 10/18/2017] [Indexed: 11/22/2022] Open
Abstract
Objective This study was conducted to investigate the efficacy of laser-assisted hatching (LAH) and various vitrification times for embryonic development and blastocyst cell numbers. Methods First, 2-cell and 8-cell embryos were collected by flushing out the oviducts. In the control groups, they were vitrified for 8 or 10 minutes without LAH. The LAH groups underwent quarter laser zona thinning-assisted hatching before vitrification (4, 6, and 8 minutes or 4, 7, and 10 minutes, respectively). After incubation, double-immunofluorescence staining was performed. Results The hatched blastocyst rate 72 hours after the 2-cell embryos were thawed was significantly higher in the 2LAH-ES8 group (33.3%) than in the other groups (p<0.05). In the control-8 group (22.1±4.6), the cell number of the inner cell mass was higher than in the LAH groups (p<0.05). The number of trophectoderm cells was higher in the 2LAH-ES6 group (92.8±8.9) than in the others (p<0.05). The hatched blastocyst rate 48 hours after the 8-cell embryos were thawed was higher in the 8LAH-ES4 group (45.5%) than in the other groups, but not significantly. The inner cell mass cell number was highest in the 8LAH-ES7 group (19.5±5.1, p<0.05). The number of trophectoderm cells was higher in the 8LAH-ES10 group (73.2±12.1) than in the other groups, but without statistical significance. Conclusion When LAH was performed, 2-cell embryos with large blastomeres had a lower hatched blastocyst rate when the exposure to vitrification solution was shorter. Conversely, 8-cell embryos with small blastomere had a higher hatched blastocyst rate when the exposure to vitrification solution was shorter.
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Affiliation(s)
- Hye Jin Kim
- Department of Obstetrics and Gynecology, Chungnam National University Hospital, Daejeon, Korea
| | - Sung Baek Park
- Mirae i Infertility Clinic, Mirae Ladies Hospital, Daejeon, Korea
| | - Jung Bo Yang
- Department of Obstetrics and Gynecology, Chungnam National University Hospital, Daejeon, Korea
| | - Young Bae Choi
- Mirae i Infertility Clinic, Mirae Ladies Hospital, Daejeon, Korea
| | - Ki Hwan Lee
- Department of Obstetrics and Gynecology, Chungnam National University Hospital, Daejeon, Korea
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Papatheodorou A, Vanderzwalmen P, Panagiotidis Y, Petousis S, Gullo G, Kasapi E, Goudakou M, Prapas N, Zikopoulos K, Georgiou I, Prapas Y. How does closed system vitrification of human oocytes affect the clinical outcome? A prospective, observational, cohort, noninferiority trial in an oocyte donation program. Fertil Steril 2016; 106:1348-1355. [DOI: 10.1016/j.fertnstert.2016.07.1066] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Revised: 06/17/2016] [Accepted: 07/11/2016] [Indexed: 12/23/2022]
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11
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[Vitrification: Principles and results]. ACTA ACUST UNITED AC 2015; 44:485-95. [PMID: 25869444 DOI: 10.1016/j.jgyn.2015.02.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Revised: 01/29/2015] [Accepted: 02/27/2015] [Indexed: 11/23/2022]
Abstract
Sperm and embryos cryopreservation is a commonly applied technique for several years. Recently authorized in France, vitrification tends to replace gradually the conventional technique of slow freezing, so upsetting the practices in the management of patients. It allows from now on the cryopreservation of oocytes and opens new perspectives in egg donation either still in fertility preservation. This review thus attempted to examine the contribution of vitrification in the freezing of oocytes and human embryos at various stages of development. If obviously vitrification appears as the current method of choice for the cryopreservation of oocytes as well as blastocysts, the results are less cut as regards embryos to early stages. No increase in adverse obstetric and perinatal outcomes in children conceived from vitrified oocytes or embryos is noted in the literature.
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12
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Wirleitner B, Vanderzwalmen P, Bach M, Baramsai B, Neyer A, Schwerda D, Schuff M, Spitzer D, Stecher A, Zintz M, Zech NH. The time aspect in storing vitrified blastocysts: its impact on survival rate, implantation potential and babies born. Hum Reprod 2013; 28:2950-7. [PMID: 24030587 DOI: 10.1093/humrep/det361] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
STUDY QUESTION Does the storage time of vitrified human blastocysts negatively impact their survival, the implantation potential of embryos or the malformation rate of babies born? SUMMARY ANSWER There was no evidence that storage times of up to 6 years after vitrification (VIT) had a negative impact on blastocyst survival, the implantation potential of embryos or the malformation rate of babies born. WHAT IS KNOWN ALREADY Although several thousand children have been born after blastocyst VIT, many aspects of this technique remain to be elucidated. New applications, such as fertility preservation, lead to long storage times of vitrified gametes or embryos but it remains to be determined if these vitrified embryos are stable over time. STUDY DESIGN, SIZE, DURATION A retrospective study including 603 transfers was conducted between January 2009 and April 2012. Blastocysts were vitrified using a closed system. PARTICIPANTS/MATERIALS, SETTING, METHODS All patients underwent the transfer of aseptically vitrified/warmed blastocysts in a cryo-cycle. A total of 1077 blastocysts were transferred. Survival rates (SRs), implantation potential, birth rates and characteristics of the children born were evaluated. MAIN RESULTS AND THE ROLE OF CHANCE We found that the storage of vitrified blastocysts in aseptic conditions neither impaired blastocyst viability (SR after warming during the first year of storage was 83.0% compared with 83.1% after 5-6 years of storage: NS) nor decreased pregnancy rates (clinical pregnancy rate after 1 year of storage was 40.0 versus 38.5% after 6 years: NS). In addition, no increase in the malformation rate over time was observed. LIMITATIONS, REASONS FOR CAUTION Our study only included the transfer of blastocysts which had been vitrified aseptically (i.e. using a closed system). Therefore, our results might not be applicable to 'open' VIT systems. The long-term follow-up of children born will be necessary to confirm our findings. WIDER IMPLICATIONS OF THE FINDINGS The results suggest that vitrified human blastocysts can be stored for long periods of time without significant negative consequences for the offspring. Therefore, the method should be of benefit to those patients who need to consider taking measures for fertility preservation. STUDY FUNDING/COMPETING INTEREST(S) No external funding was sought for this study and the authors have no conflict of interest to declare.
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Affiliation(s)
- B Wirleitner
- IVF Centers Prof. Zech - Bregenz, Römerstrasse 2, 6900 Bregenz, Austria
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Panagiotidis Y, Vanderzwalmen P, Prapas Y, Kasapi E, Goudakou M, Papatheodorou A, Passadaki T, Petousis S, Nikolettos N, Veletza S, Prapas N, Maroulis G. Open versus closed vitrification of blastocysts from an oocyte-donation programme: a prospective randomized study. Reprod Biomed Online 2013; 26:470-6. [DOI: 10.1016/j.rbmo.2013.01.016] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Revised: 01/23/2013] [Accepted: 01/24/2013] [Indexed: 10/27/2022]
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Zheng H, Chen Y, Lu F, Liu M, Yang X, Fu X, Zhao Y, Huang B, Huang S, Kasper LH. Cryopreservation of Toxoplasma gondii in infected murine tissues. Parasitol Res 2012; 111:2449-53. [DOI: 10.1007/s00436-012-2991-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Accepted: 05/29/2012] [Indexed: 10/28/2022]
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15
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Clinical validation of a closed vitrification system in an oocyte-donation programme. Reprod Biomed Online 2012; 24:180-5. [DOI: 10.1016/j.rbmo.2011.10.015] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 09/07/2011] [Accepted: 10/20/2011] [Indexed: 11/24/2022]
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16
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Parmegiani L, Cognigni GE, Bernardi S, Cuomo S, Ciampaglia W, Infante FE, Tabarelli de Fatis C, Arnone A, Maccarini AM, Filicori M. Efficiency of aseptic open vitrification and hermetical cryostorage of human oocytes. Reprod Biomed Online 2011; 23:505-12. [PMID: 21843968 DOI: 10.1016/j.rbmo.2011.07.003] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Revised: 06/29/2011] [Accepted: 07/01/2011] [Indexed: 11/17/2022]
Abstract
The present study reports, as far as is known for the first time, the safety of UV sterilization of liquid nitrogen and hermetical cryostorage of human oocytes by comparing the efficiency of fresh and vitrified sibling oocytes of infertile patients. A prospective randomized study on sibling oocytes of 31 patients was carried out. Metaphase-II oocytes were randomized for intracytoplasmic sperm injection and the supernumerary sibling oocytes were vitrified using a novel Cryotop aseptic procedure (UV liquid nitrogen sterilization and hermetical cryostorage). After unsuccessful attempts with fresh oocytes, vitrified sibling oocytes were injected. Mean outcome measures observed were fertilization, cleavage and top-quality embryo rates. No significant differences were observed between the fresh and vitrified-warmed sibling oocytes: oocyte fertilization was 88.3% versus 84.9%; cleavage 72.6% versus 71.0%; top-quality embryos 33.8% versus 26.3% and mean number of transferred embryos 2.6 ± 0.1 versus 2.5 ± 0.1, respectively. Clinical pregnancy rate per cycle with vitrified-warmed oocytes was 35.5% (implantation rate 17.1%) and seven healthy babies were born. This study demonstrated that UV liquid nitrogen sterilization and hermetical cryostorage does not adversely affect the developmental competence of vitrified oocytes, allowing safe aseptic open vitrification applicable under strict directives on tissue manipulation.
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Affiliation(s)
- L Parmegiani
- Reproductive Medicine Unit, GynePro Medical Centers, Bologna, Italy.
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AbdelHafez F, Xu J, Goldberg J, Desai N. Vitrification in open and closed carriers at different cell stages: assessment of embryo survival, development, DNA integrity and stability during vapor phase storage for transport. BMC Biotechnol 2011; 11:29. [PMID: 21450077 PMCID: PMC3079628 DOI: 10.1186/1472-6750-11-29] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Accepted: 03/30/2011] [Indexed: 12/03/2022] Open
Abstract
Background High cooling rates with vitrification can be achieved through the use of carriers that allow cryopreservation in fluid volumes < one μl. Open carriers allow direct contact of embryos with liquid nitrogen (LN2) whereas closed carrier systems sequester the embryo within a sealed system during immersion in LN2. The use of closed systems may be preferable to reduce the possibility of cross-contamination. In the present study, we compare open and closed carriers for vitrification of embryos. We also examine their ability to retain embryo viability during vapor phase transport. Methods Frozen one-cell mouse embryos were thawed and randomly allocated to treatment groups. Embryos were cultured and vitrified at the 8-cell (CL) or at the blastocyst (BL) stage. The cryoloop, an open carrier was tested against two closed systems, the Cryotip and the HSV straw. Carriers were tested for their ability to maintain embryo viability when held in the vapor phase of a dry shipper for a period of 96 hours. Outcome parameters monitored were embryo survival, recovery, subsequent development and signs of DNA damage. Results A total of 561 embryos were vitrified. The only parameter significantly affected by the type of carrier was the percentage of embryos recovered after warming. Vitrification of both CL and BL stage embryos in the Cryotip resulted in significantly lower recovery rates (P < 0.001). The subsequent developmental parameters were unaffected by either the carrier or the cell stage. Vapor phase storage for 96 hours under "transport conditions" did not appear to adversely affect the viability after warming. Quantitative analysis for DNA damage showed that <5% of cells were TUNEL positive. Interestingly, the overall percent of cells exhibiting DNA damage was lower after CL stage vitrification (P < 0.001). Conclusion This study is one of the first to examine DNA integrity after vitrification on different carriers and at different cell stages. It also provides insight on relative safety of short term vapor storage of vitrified embryos during transport. Within the limits of this study we could not detect an adverse effect of vapor storage on blastomere DNA or other measured outcome parameters.
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Affiliation(s)
- Faten AbdelHafez
- Cleveland Clinic Fertility Center, Department of OB/GYN and Women's Health Institute, Cleveland Clinic Foundation, USA
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Boldt J. Current results with slow freezing and vitrification of the human oocyte. Reprod Biomed Online 2010; 23:314-22. [PMID: 21592862 DOI: 10.1016/j.rbmo.2010.11.019] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Revised: 10/07/2010] [Accepted: 11/23/2010] [Indexed: 01/23/2023]
Abstract
The past decade has witnessed renewed interest in human oocyte cryopreservation (OCP). This article reviews the two general methods used for OCP, slow freezing and vitrification, compares the outcomes associated with each technique and discusses the factors that might influence success with OCP (such as oocyte selection or day of transfer). Based on available data, OCP offers a reliable, reproducible method for preservation of the female gamete and will find increasing application in assisted reproductive technology. Oocyte cryopreservation can provide a number of advantages to couples undergoing assisted reproduction or to women interested in fertility preservation. Two methods, slow freezing and vitrification, have been used successfully for oocyte cryopreservation. This article reviews and compares these methods, and discusses various factors that can impact upon success of oocyte cryopreservation.
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Affiliation(s)
- Jeffrey Boldt
- Assisted Fertility Services, Community Health Network, 8040 Clearvista Parkway, Indianapolis, IN 46256, USA.
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Effect of liquid nitrogen vapor storage on the motility, viability, morphology, deoxyribonucleic acid integrity, and mitochondrial potential of frozen-thawed human spermatozoa. Fertil Steril 2010; 94:2736-41. [DOI: 10.1016/j.fertnstert.2010.02.051] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2009] [Revised: 02/06/2010] [Accepted: 02/23/2010] [Indexed: 11/23/2022]
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Cobo A, Romero JL, Pérez S, de los Santos MJ, Meseguer M, Remohí J. Storage of human oocytes in the vapor phase of nitrogen. Fertil Steril 2010; 94:1903-7. [DOI: 10.1016/j.fertnstert.2009.10.042] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2009] [Revised: 10/26/2009] [Accepted: 10/26/2009] [Indexed: 10/19/2022]
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Parmegiani L, Accorsi A, Cognigni GE, Bernardi S, Troilo E, Filicori M. Sterilization of liquid nitrogen with ultraviolet irradiation for safe vitrification of human oocytes or embryos. Fertil Steril 2010; 94:1525-1528. [DOI: 10.1016/j.fertnstert.2009.05.089] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 05/14/2009] [Accepted: 05/21/2009] [Indexed: 10/20/2022]
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Lee JY, Lee JE, Kim DK, Yoon TK, Chung HM, Lee DR. High concentration of synthetic serum, stepwise equilibration and slow cooling as an efficient technique for large-scale cryopreservation of human embryonic stem cells. Fertil Steril 2008; 93:976-85. [PMID: 19022437 DOI: 10.1016/j.fertnstert.2008.10.017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2008] [Revised: 09/29/2008] [Accepted: 10/07/2008] [Indexed: 01/03/2023]
Abstract
OBJECTIVE To develop an efficient freezing method suitable for large-scale cryopreservation of human embryonic stem cells (hESCs). DESIGN Experimental study. SETTING Research institute. PATIENT(S) None. INTERVENTION(S) Two genetically modified hESC lines, H9-EF1-GFP and CHA-hES3-EF1-GFP, were cryopreserved in cryovials using a combination of two equilibration methods (one-step and stepwise) and two cooling vehicles (cryo-container and program-controlled freezer). After thawing, the survival and differentiation rate were compared among groups. MAIN OUTCOME MEASURE(S) The hESC survival was assessed by alkaline phosphatase staining and differentiation status was determined by flow cytometry using an SSEA-4 antibody. RESULT(S) In both H9-EF1-GFP and CHA-hES3-EF1-GFP cells, the survival rate was highest in the group using stepwise equilibration and program-controlled freezer, and lowest in the group using one-step equilibration and cryo-container. In the groups using cryo-container, the survival and the frequency of undifferentiated cells in both cell lines was highly improved in a stepwise equilibration compared with one-step. Thawed hESCs were positively stained with pluripotent markers SSEA-4, TRA-1-60, TRA-1-81, and alkaline phosphatase. The karyotypes and expression of three germ layer markers in both cell lines were not changed after freezing/thawing. CONCLUSION(S) The stepwise equilibration of Knockout Serum Replacement and cryoprotectant during freezing and thawing resulted in higher survival rates by reducing osmotic damage irrespective of cooling vehicles.
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Affiliation(s)
- Ji Yeon Lee
- Fertility Center, CHA General Hospital, CHA Research Institute, Pochon CHA University, Seoul 135-081, South Korea
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