{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,31]],"date-time":"2026-01-31T20:31:11Z","timestamp":1769891471709,"version":"3.49.0"},"reference-count":47,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,1,29]],"date-time":"2026-01-29T00:00:00Z","timestamp":1769644800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Jeweler A. L. Rasmussen & D Wife Foundation"},{"DOI":"10.13039\/501100003035","name":"Aase and Ejnar Danielsens Foundation","doi-asserted-by":"crossref","id":[{"id":"10.13039\/501100003035","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Merck"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JCM"],"abstract":"<jats:p>Background\/Objectives: Cryopreservation technology used in assisted reproductive technology (ART) has significantly improved live birth rates by enabling multiple embryo transfers with frozen embryos from a single ovarian stimulation cycle. However, there is conflicting data on the effect of prolonged cryopreservation of human blastocysts. Methods: This Danish nationwide cohort study includes all frozen embryo transfers (FETs) from 1 January 2012 to 31 March 2019. Biochemical pregnancy, clinical pregnancy, and live births were analyzed based on blastocyst storage time. Blastocyst storage time was stratified into five groups, \u22643 month, 4\u20136 months, 7\u201312 months, 13\u201324 months, and \u226525 months, with the shortest (\u22643 months) as the reference. We also examined the risk of preterm birth, small and large for gestational age (SGA and LGA), and congenital malformations among live-born children. Multivariable analysis was used to estimate the odd ratios of the reproductive outcomes, accounting for potential confounders. Results: We identified 7042 women with 12,599 FETs. Characteristics of women at embryo transfer did not vary significantly by storage time, except for polycystic ovarian syndrome (PCOS), which increased from 2.6% in the reference group to 6.7% in the \u226525-month group. The clinical pregnancy rate was 35.7%. Blastocyst storage time did not significantly affect biochemical pregnancy rates, with adjusted odds ratios (aORs) of 0.94 (95% CI: 0.80\u20131.11) to 0.96 (95% CI: 0.82\u20131.12) for the 13\u201324-month and \u226525-month groups, respectively. Clinical pregnancy rates also did not decrease with storage time (aOR 0.96, 95% CI: 0.82\u20131.13) for \u226525 months. The live birth rate was 28.6%, with no significant decrease during storage (aOR 0.89, 95% CI: 0.75\u20131.06). However, the risk of LGA was slightly, but non-significantly, increased (aOR: 1.42, 95% CI: 0.84\u20132.42) in the \u226525-month group, whereas the aOR of SGA and congenital malformations was not increased. Conclusions: Our data indicates that storing blastocysts for a period of 25 months does not significantly affect pregnancy chances following assisted reproductive technology treatment.<\/jats:p>","DOI":"10.3390\/jcm15031072","type":"journal-article","created":{"date-parts":[[2026,1,29]],"date-time":"2026-01-29T12:49:07Z","timestamp":1769690947000},"page":"1072","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Does Prolonged Preservation of Blastocysts Affect the Implantation and Live Birth Rate? A Danish Nationwide Register-Based Study"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5264-6434","authenticated-orcid":false,"given":"Tilde Veng","family":"Eskildsen","sequence":"first","affiliation":[{"name":"Fertility Clinic, Odense University Hospital, 5000 Odense, Denmark"},{"name":"Clinical Research Unit of Gynaecology and Obstetrics, Institute of Clinical Research, University of Southern Denmark, 5000 Odense, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0623-2481","authenticated-orcid":false,"given":"Michael Due","family":"Larsen","sequence":"additional","affiliation":[{"name":"Center for Clinical Epidemiology, Odense University Hospital, 5000 Odense, Denmark"},{"name":"Department of Clinical and Molecular Medicine, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, 7491 Trondheim, Norway"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5383-5501","authenticated-orcid":false,"given":"Jens","family":"Fedder","sequence":"additional","affiliation":[{"name":"Fertility Clinic, Odense University Hospital, 5000 Odense, Denmark"},{"name":"Clinical Research Unit of Gynaecology and Obstetrics, Institute of Clinical Research, University of Southern Denmark, 5000 Odense, Denmark"},{"name":"Centre of Andrology & Fertility Clinic, Horsens Hospital & Aarhus University, 8700 Horsens, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7433-7656","authenticated-orcid":false,"given":"Line Riis","family":"J\u00f8lving","sequence":"additional","affiliation":[{"name":"Center for Clinical Epidemiology, Odense University Hospital, 5000 Odense, Denmark"},{"name":"Research Unit of Clinical Epidemiology, University of Southern Denmark, 5000 Odense, Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,29]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"707","DOI":"10.1038\/305707a0","article-title":"Human pregnancy following cryopreservation, thawing and transfer of an eight-cell embryo","volume":"305","author":"Trounson","year":"1983","journal-title":"Nature"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"119","DOI":"10.1016\/j.repbio.2019.04.002","article-title":"Ice age: Cryopreservation in assisted reproduction\u2014An update","volume":"19","author":"Waterstone","year":"2019","journal-title":"Reprod. 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