{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,4]],"date-time":"2025-12-04T06:59:39Z","timestamp":1764831579389,"version":"3.46.0"},"reference-count":62,"publisher":"MDPI AG","issue":"23","license":[{"start":{"date-parts":[[2025,12,2]],"date-time":"2025-12-02T00:00:00Z","timestamp":1764633600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"IVIRMA Barcelona and IVI Foundation","award":["1701-BCN-007-EL"],"award-info":[{"award-number":["1701-BCN-007-EL"]}]},{"DOI":"10.13039\/501100004587","name":"Instituto de Salud Carlos III (ISCIII), Spanish Ministry of Science and Innovation","doi-asserted-by":"publisher","award":["PI21\/00310","CP20\/00118"],"award-info":[{"award-number":["PI21\/00310","CP20\/00118"]}],"id":[{"id":"10.13039\/501100004587","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100000780","name":"European Union","doi-asserted-by":"crossref","award":["BIRTH Grant 2021"],"award-info":[{"award-number":["BIRTH Grant 2021"]}],"id":[{"id":"10.13039\/501100000780","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nutrients"],"abstract":"<jats:p>Background\/Objectives: One of the main reasons for discrepancies in the role of vitamin D in ART could be the measurement of the conventional biomarker 25(OH)D3. It is known that this value is affected by multiple factors, such as tissue origin, assay variability, classification criteria, and potential storage-related degradation. In this study, we investigate 24,25(OH)2D3 as a new biomarker to improve vitamin D assessment in women\u2019s reproductive health, particularly regarding oocyte development. Methods: A prospective cohort study including 35 oocyte donors undergoing controlled ovarian stimulation, who were recruited between October and November 2017, was conducted. Vitamin D metabolites were measured at the baseline and after seven months of storage at \u221280 \u00b0C. Paired serum and pooled follicular fluid (FF) samples were collected at oocyte retrieval. 25(OH)D3 and 24,25(OH)2D3 were quantified by ultra-performance liquid chromatography\u2013tandem mass spectrometry (UPLC\u2013MS\/MS). Statistical analyses included paired tests (serum vs. FF; baseline vs. stored) and Pearson\u2019s correlations (two-sided \u03b1 = 0.05). Results: At the baseline, the mean serum 25(OH)D3 concentration was 91.56 \u00b1 39.01 nmol\/L and the mean FF concentration was 58.13 \u00b1 19.55 nmol\/L (p &lt; 0.0001). Serum 24,25(OH)2D3 averaged 15.62 \u00b1 10.99 nmol\/L, compared with 11.26 \u00b1 6.09 nmol\/L in FF (p = 0.004). In both fluids, 25(OH)D3 and 24,25(OH)2D3 were strongly correlated (serum R2 = 0.92; FF R2 = 0.91). Across fluids, the serum\u2013FF correlation was stronger for 24,25(OH)2D3 (R2 = 0.77, p &lt;0.0001) than for 25(OH)D3 (R2 = 0.69, p &lt; 0.0001). After seven months of storage, 25(OH)D3 concentrations decreased significantly (serum \u221232%; FF \u221238%; both p &lt; 0.0001), whereas 24,25(OH)2D3 levels remained stable (serum p = 0.24; FF p = 0.36). Conclusions: Serum 24,25(OH)2D3 is a more reliable and minimally invasive biomarker for assessing ovarian vitamin D status than the current gold standard, 25(OH)D3. Incorporating this metabolite into research studies and storage quality control may improve the reliability of retrospective analyses based on cryopreserved material, contributing to a better understanding of the role of vitamin D in human reproduction.<\/jats:p>","DOI":"10.3390\/nu17233783","type":"journal-article","created":{"date-parts":[[2025,12,3]],"date-time":"2025-12-03T10:34:01Z","timestamp":1764758041000},"page":"3783","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Reducing Storage-Related Bias in Reproductive Vitamin D Research: Towards a Stable and Reliable Biomarker of Ovarian Vitamin D Status"],"prefix":"10.3390","volume":"17","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-7564-1943","authenticated-orcid":false,"given":"Evelin E.","family":"Lara-Molina","sequence":"first","affiliation":[{"name":"IVIRMA Global Research Alliance, IVIRMA Barcelona, 08029 Barcelona, Spain"},{"name":"IVI Foundation, Instituto de Investigaci\u00f3n Sanitaria La Fe (IIS La Fe), 46026 Valencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5595-1263","authenticated-orcid":false,"given":"Jason M.","family":"Franasiak","sequence":"additional","affiliation":[{"name":"IVIRMA Global Research Alliance, Reproductive Medicine Associates of New Jersey, Basking Ridge, NJ 07920, USA"},{"name":"Sidney Kimmel Medical School, Thomas Jefferson University, Philadelphia, PA 19107, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5540-3032","authenticated-orcid":false,"given":"Almudena","family":"Devesa-Peiro","sequence":"additional","affiliation":[{"name":"IVI Foundation, Instituto de Investigaci\u00f3n Sanitaria La Fe (IIS La Fe), 46026 Valencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3114-2231","authenticated-orcid":false,"given":"Marina","family":"L\u00f3pez-Nogueroles","sequence":"additional","affiliation":[{"name":"Instituto de Investigaci\u00f3n Sanitaria La Fe (IIS La Fe), 46026 Valencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0007-4249-1660","authenticated-orcid":false,"given":"Alberto","family":"V\u00e1zquez","sequence":"additional","affiliation":[{"name":"IVIRMA Global Research Alliance, IVIRMA Barcelona, 08029 Barcelona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0007-0669-5017","authenticated-orcid":false,"given":"David","family":"Amor\u00f3s","sequence":"additional","affiliation":[{"name":"IVIRMA Global Research Alliance, IVIRMA Barcelona, 08029 Barcelona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3097-3498","authenticated-orcid":false,"given":"Agust\u00edn","family":"Ballesteros","sequence":"additional","affiliation":[{"name":"IVIRMA Global Research Alliance, IVIRMA Barcelona, 08029 Barcelona, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3316-7619","authenticated-orcid":false,"given":"Antonio","family":"Pellicer","sequence":"additional","affiliation":[{"name":"IVIRMA Global Research Alliance, IVIRMA Roma, 00161 Rome, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7299-3660","authenticated-orcid":false,"given":"Patricia","family":"Sebastian-Leon","sequence":"additional","affiliation":[{"name":"IVI Foundation, Instituto de Investigaci\u00f3n Sanitaria La Fe (IIS La Fe), 46026 Valencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0031-7545","authenticated-orcid":false,"given":"Patricia","family":"Diaz-Gimeno","sequence":"additional","affiliation":[{"name":"IVI Foundation, Instituto de Investigaci\u00f3n Sanitaria La Fe (IIS La Fe), 46026 Valencia, Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,12,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"317","DOI":"10.1038\/281317a0","article-title":"1 Alpha, 25-Dihydroxyvitamin D3 and 24,25-Dihydroxyvitamin D3 in Vitro Synthesis by Human Decidua and Placenta","volume":"281","author":"Weisman","year":"1979","journal-title":"Nature"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1188","DOI":"10.1126\/science.505004","article-title":"Target Cells for 1,25-Dihydroxyvitamin D3 in Intestinal Tract, Stomach, Kidney, Skin, Pituitary, and Parathyroid","volume":"206","author":"Stumpf","year":"1979","journal-title":"Science"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"200","DOI":"10.1210\/endo-112-1-200","article-title":"The Ovary: A Target Organ for 1,25-Dihydroxyvitamin D3","volume":"112","author":"Dokoh","year":"1983","journal-title":"Endocrinology"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"7","DOI":"10.1007\/BF01450873","article-title":"Immunohistochemical Detection and Distribution of the 1,25-Dihydroxyvitamin D3 Receptor in Rat Reproductive Tissues","volume":"105","author":"Johnson","year":"1996","journal-title":"Histochem. Cell Biol."},{"key":"ref_5","first-page":"e65560","article-title":"The Key Role of Vitamin D in Female Reproductive Health: A Narrative Review","volume":"16","author":"Dragomir","year":"2024","journal-title":"Cureus"},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"\u0141agowska, K. (2018). The Relationship between Vitamin D Status and the Menstrual Cycle in Young Women: A Preliminary Study. Nutrients, 10.","DOI":"10.3390\/nu10111729"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"754","DOI":"10.1055\/s-0030-1262837","article-title":"Vitamin D Regulates Steroidogenesis and Insulin-like Growth Factor Binding Protein-1 (IGFBP-1) Production in Human Ovarian Cells","volume":"42","author":"Parikh","year":"2010","journal-title":"Horm. Metab. Res."},{"key":"ref_8","first-page":"979","article-title":"Association between Serum 25-Hydroxy Vitamin D Level and Menstrual Cycle Length and Regularity: A Cross-Sectional Observational Study","volume":"19","author":"Singh","year":"2021","journal-title":"Int. J. Reprod. Biomed."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"E1137","DOI":"10.1210\/jc.2013-4161","article-title":"Vitamin D Alters Genes Involved in Follicular Development and Steroidogenesis in Human Cumulus Granulosa Cells","volume":"99","author":"Merhi","year":"2014","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"e210444","DOI":"10.1530\/EC-21-0444","article-title":"100 YEARS OF VITAMIN D: Effect of Serum Vitamin D Level before Ovarian Stimulation on the Cumulative Live Birth Rate of Women Undergoing in Vitro Fertilization: A Retrospective Analysis","volume":"11","author":"Ko","year":"2022","journal-title":"Endocr. Connect."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Grundmann, M., and Von Versen-H\u00f6ynck, F. (2011). Vitamin D\u2014Roles in Women\u2019s Reproductive Health?. Reprod. Biol. Endocrinol., 9.","DOI":"10.1186\/1477-7827-9-146"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Tahsin, T., Khanam, R., Chowdhury, N.H., Hasan, A.S.M.T., Hosen, M.D.B., Rahman, S., Roy, A.K., Ahmed, S., Raqib, R., and Baqui, A.H. (2023). Vitamin D Deficiency in Pregnancy and the Risk of Preterm Birth: A Nested Case\u2013Control Study. BMC Pregnancy Childbirth, 23.","DOI":"10.1186\/s12884-023-05636-z"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Van Tienhoven, X.A., Ruiz De Ch\u00e1vez Gasc\u00f3n, J., Cano-Herrera, G., Sarkis Nehme, J.A., Souroujon Torun, A.A., Bautista Gonzalez, M.F., Esparza Salazar, F., Sierra Brozon, A., Rivera Rosas, E.G., and Carbajal Ocampo, D. (2025). Vitamin D in Reproductive Health Disorders: A Narrative Review Focusing on Infertility, Endometriosis, and Polycystic Ovarian Syndrome. Int. J. Mol. Sci., 26.","DOI":"10.20944\/preprints202502.0237.v1"},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Arnanz, A., De Munck, N., El Khatib, I., Bayram, A., Abdala, A., Melado, L., Lawrenz, B., Coughlan, C., Pacheco, A., and Garcia-Velasco, J.A. (2021). Vitamin D in Follicular Fluid Correlates With the Euploid Status of Blastocysts in a Vitamin D Deficient Population. Front. Endocrinol., 11.","DOI":"10.3389\/fendo.2020.609524"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"00368504221103782","DOI":"10.1177\/00368504221103782","article-title":"The Level of Vitamin D in Follicular Fluid and Ovarian Reserve in an in Vitro Fertilization Program: A Pilot Study","volume":"105","author":"Han","year":"2022","journal-title":"Sci. Progress."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"620","DOI":"10.1016\/j.tjog.2022.03.041","article-title":"Follicular Fluid 25-Hydroxyvitamin D Levels Determine Fertility Outcome in Patients with Polycystic Ovary Syndrome","volume":"61","author":"Ozyurt","year":"2022","journal-title":"Taiwan. J. Obstet. Gynecol."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1418","DOI":"10.5114\/aoms\/141185","article-title":"Follicular and Serum Levels of Vitamin D in Women with Unexplained Infertility and Their Relationship with in Vitro Fertilization Outcome: An Observational Pilot Study","volume":"17","author":"Jeremic","year":"2021","journal-title":"Arch. Med. Sci."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Putri Susilo, A.F., Syam, H.H., Bayuaji, H., Rachmawati, A., Halim, B., Permadi, W., and Djuwantono, T. (2024). Free 25(OH)D3 Levels in Follicular Ovarian Fluid Top-Quality Embryos Are Higher than Non-Top-Quality Embryos in the Normoresponders Group. Sci. Rep., 14.","DOI":"10.1038\/s41598-024-71769-6"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"439","DOI":"10.1007\/s001980050030","article-title":"Prevalence of Vitamin D Insufficiency in an Adult Normal Population","volume":"7","author":"Chapuy","year":"1997","journal-title":"Osteoporos. Int."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"323","DOI":"10.1007\/s10815-014-0407-9","article-title":"Vitamin D and Assisted Reproduction: Should Vitamin D Be Routinely Screened and Repleted Prior to ART? A Systematic Review","volume":"32","author":"Pacis","year":"2015","journal-title":"J. Assist. Reprod. Genet."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"65","DOI":"10.1093\/humrep\/dex326","article-title":"Vitamin D and Assisted Reproductive Treatment Outcome: A Systematic Review and Meta-Analysis","volume":"33","author":"Chu","year":"2018","journal-title":"Human. Reprod."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1033","DOI":"10.3945\/ajcn.115.120873","article-title":"Vitamin D Deficiency in Europe: Pandemic?","volume":"103","author":"Cashman","year":"2016","journal-title":"Am. J. Clin. Nutr."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"S13","DOI":"10.1016\/j.bone.2007.03.010","article-title":"Where Do We Stand on Vitamin D?","volume":"41","author":"Bischoffferrari","year":"2007","journal-title":"Bone"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"2997","DOI":"10.1210\/jc.2011-1193","article-title":"The Effect of Vitamin D on Falls: A Systematic Review and Meta-Analysis","volume":"96","author":"Murad","year":"2011","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"625","DOI":"10.1210\/endrev\/bnae009","article-title":"Consensus Statement on Vitamin D Status Assessment and Supplementation: Whys, Whens, and Hows","volume":"45","author":"Giustina","year":"2024","journal-title":"Endocr. Rev."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"486","DOI":"10.1373\/clinchem.2011.180562","article-title":"25-Hydroxyvitamin D: A Difficult Analyte","volume":"58","author":"Carter","year":"2012","journal-title":"Clin. Chem."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"331","DOI":"10.2215\/CJN.05490614","article-title":"Interpreting Vitamin D Assay Results: Proceed with Caution","volume":"10","author":"Jones","year":"2015","journal-title":"Clin. J. Am. Soc. Nephrol."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Yu, S., Cheng, X., Fang, H., Zhang, R., Han, J., Qin, X., Cheng, Q., Su, W., Hou, L., and Xia, L. (2015). 25OHD Analogues and Vacuum Blood Collection Tubes Dramatically Affect the Accuracy of Automated Immunoassays. Sci. Rep., 5.","DOI":"10.1038\/srep14636"},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Ferrari, D., Lombardi, G., and Banfi, G. (2017). Concerning the Vitamin D Reference Range: Pre-Analytical and Analytical Variability of Vitamin D Measurement. Biochem. Medica, 27.","DOI":"10.11613\/BM.2017.030501"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"42","DOI":"10.1097\/00001648-199401000-00008","article-title":"Racial differences in fracture risk","volume":"5","author":"Baron","year":"1994","journal-title":"Epidemiology"},{"key":"ref_31","first-page":"4125","article-title":"Vitamin D Insufficiency and Hyperparathyroidism in a Low Income, Multiracial, Elderly Population1","volume":"85","author":"Harris","year":"2000","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"485","DOI":"10.1093\/ajcn\/78.3.485","article-title":"Association of Low 25-Hydroxyvitamin D Concentrations with Elevated Parathyroid Hormone Concentrations and Low Cortical Bone Density in Early Pubertal and Prepubertal Finnish Girls","volume":"78","author":"Cheng","year":"2003","journal-title":"Am. J. Clin. Nutr."},{"key":"ref_33","doi-asserted-by":"crossref","unstructured":"Bouillon, R., Schuit, F., Antonio, L., and Rastinejad, F. (2020). Vitamin D Binding Protein: A Historic Overview. Front. Endocrinol., 10.","DOI":"10.3389\/fendo.2019.00910"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"773","DOI":"10.1093\/clinchem\/27.5.773","article-title":"Stability of Vitamin D Metabolites in Human Blood Serum and Plasma","volume":"27","author":"Lissner","year":"1981","journal-title":"Clin. Chem."},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Ko, J.K.Y., Chen, S.P.L., Lam, K.K.W., Chan, T.O., Li, R.H.W., and Ng, E.H.Y. (2025). Effect of Freezing and Storage on Serum Vitamin D Levels Measured by Mass Spectrometry and Immunoassay in Reproductive Age Women. Sci. Rep., 15.","DOI":"10.1038\/s41598-025-02811-4"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1917","DOI":"10.1007\/s00216-008-2095-8","article-title":"Metabolic Profiling of Major Vitamin D Metabolites Using Diels\u2013Alder Derivatization and Ultra-Performance Liquid Chromatography\u2013Tandem Mass Spectrometry","volume":"391","author":"Aronov","year":"2008","journal-title":"Anal. Bioanal. Chem."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"5615","DOI":"10.1007\/s00216-015-8733-z","article-title":"A Candidate Reference Measurement Procedure for Quantifying Serum Concentrations of 25-Hydroxyvitamin D3 and 25-Hydroxyvitamin D2 Using Isotope-Dilution Liquid Chromatography-Tandem Mass Spectrometry","volume":"407","author":"Mineva","year":"2015","journal-title":"Anal. Bioanal. Chem."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1244","DOI":"10.5740\/jaoacint.17-0258","article-title":"Baseline Assessment of 25-Hydroxyvitamin D Assay Performance: A Vitamin D Standardization Program (VDSP) Interlaboratory Comparison Study","volume":"100","author":"Wise","year":"2017","journal-title":"J. AOAC Int."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1515\/cclm-2016-0264","article-title":"Assessment of Vitamin D Status\u2014A Changing Landscape","volume":"55","author":"Herrmann","year":"2017","journal-title":"Clin. Chem. Lab. Med."},{"key":"ref_40","unstructured":"Ross, A.C., Taylor, C.L., Yaktine, A.L., and Del Valle, H.B. (2011). Dietary Reference Intakes for Calcium and Vitamin D, National Academies Press."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"1911","DOI":"10.1210\/jc.2011-0385","article-title":"Evaluation, Treatment, and Prevention of Vitamin D Deficiency: An Endocrine Society Clinical Practice Guideline","volume":"96","author":"Holick","year":"2011","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"1907","DOI":"10.1210\/clinem\/dgae290","article-title":"Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline","volume":"109","author":"Demay","year":"2024","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"2567","DOI":"10.1210\/jc.2013-4388","article-title":"Clinical Utility of Simultaneous Quantitation of 25-Hydroxyvitamin D and 24,25-Dihydroxyvitamin D by LC-MS\/MS Involving Derivatization with DMEQ-TAD","volume":"99","author":"Kaufmann","year":"2014","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"21","DOI":"10.1016\/j.jnutbio.2017.04.005","article-title":"Reference Intervals for Serum 24,25-Dihydroxyvitamin D and the Ratio with 25-Hydroxyvitamin D Established Using a Newly Developed LC\u2013MS\/MS Method","volume":"46","author":"Tang","year":"2017","journal-title":"J. Nutr. Biochem."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"1","DOI":"10.18637\/jss.v017.i03","article-title":"The Strucplot Framework: Visualizing Multi-Way Contingency Tables with Vcd","volume":"17","author":"Meyer","year":"2006","journal-title":"J. Stat. Soft."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"276","DOI":"10.11613\/BM.2012.031","article-title":"Interrater Reliability: The Kappa Statistic","volume":"22","author":"McHugh","year":"2012","journal-title":"Biochem. Med."},{"key":"ref_47","unstructured":"R Core Team (2021). R: A Language and Environment for Statistical Computing, R Foundation for Statistical Computing."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"1314","DOI":"10.1016\/j.fertnstert.2009.05.019","article-title":"Replete Vitamin D Stores Predict Reproductive Success Following in Vitro Fertilization","volume":"94","author":"Ozkan","year":"2010","journal-title":"Fertil. Steril."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"3321","DOI":"10.1093\/humrep\/des280","article-title":"Characterizing the Influence of Vitamin D Levels on IVF Outcomes","volume":"27","author":"Rudick","year":"2012","journal-title":"Human. Reprod."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"1339","DOI":"10.1007\/s00404-016-4058-1","article-title":"Serum Vitamin D Status and in Vitro Fertilization Outcomes: A Systematic Review and Meta-Analysis","volume":"293","author":"Lv","year":"2016","journal-title":"Arch. Gynecol. Obstet."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"3027","DOI":"10.1210\/jc.2015-4352","article-title":"Vitamin D Status Relates to Reproductive Outcome in Women With Polycystic Ovary Syndrome: Secondary Analysis of a Multicenter Randomized Controlled Trial","volume":"101","author":"Pal","year":"2016","journal-title":"J. Clin. Endocrinol. Metab."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"132","DOI":"10.1016\/j.ejogrb.2011.07.006","article-title":"Predictive Value of the Level of Vitamin D in Follicular Fluid on the Outcome of Assisted Reproductive Technology","volume":"159","author":"Aleyasin","year":"2011","journal-title":"Eur. J. Obstet. Gynecol. Reprod. Biol."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"315.e1","DOI":"10.1016\/j.ajog.2014.09.029","article-title":"Vitamin D Levels Do Not Affect IVF Outcomes Following the Transfer of Euploid Blastocysts","volume":"212","author":"Franasiak","year":"2015","journal-title":"Am. J. Obstet. Gynecol."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"201","DOI":"10.1007\/s00404-013-2959-9","article-title":"Value of Follicular Fluid Vitamin D in Predicting the Pregnancy Rate in an IVF Program","volume":"289","author":"Firouzabadi","year":"2014","journal-title":"Arch. Gynecol. Obstet."},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"1749","DOI":"10.1093\/humrep\/dew107","article-title":"Vitamin D Deficiency and Pregnancy Rates Following Frozen\u2013Thawed Embryo Transfer: A Prospective Cohort Study","volume":"31","author":"Drakopoulos","year":"2016","journal-title":"Hum. Reprod."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"139","DOI":"10.1016\/j.rbmo.2017.05.009","article-title":"Impact of Vitamin D Levels on Ovarian Reserve and Ovarian Response to Ovarian Stimulation in Oocyte Donors","volume":"35","author":"Fabris","year":"2017","journal-title":"Reprod. Biomed. Online"},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"531","DOI":"10.1373\/clinchem.2011.172155","article-title":"State-of-the-Art Vitamin D Assays: A Comparison of Automated Immunoassays with Liquid Chromatography\u2013Tandem Mass Spectrometry Methods","volume":"58","author":"Farrell","year":"2012","journal-title":"Clin. Chem."},{"key":"ref_58","first-page":"32","article-title":"Vitamin D Status as an International Issue: National Surveys and the Problem of Standardization","volume":"243","author":"Sempos","year":"2012","journal-title":"Scand. J. Clin. Lab. Investig."},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"1709","DOI":"10.1002\/jbmr.2252","article-title":"Standardizing Vitamin D Assays: The Way Forward","volume":"29","author":"Binkley","year":"2014","journal-title":"J. Bone Miner. Res."},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"30","DOI":"10.1016\/j.jsbmb.2017.07.018","article-title":"Hydroxyvitamin D Assays: An Historical Perspective from DEQAS","volume":"177","author":"Carter","year":"2018","journal-title":"J. Steroid Biochem. Mol. Biol."},{"key":"ref_61","doi-asserted-by":"crossref","first-page":"189","DOI":"10.1097\/GCO.0000000000000375","article-title":"Vitamin D in Human Reproduction","volume":"29","author":"Franasiak","year":"2017","journal-title":"Curr. Opin. Obstet. Gynecol."},{"key":"ref_62","doi-asserted-by":"crossref","first-page":"2511","DOI":"10.1007\/s00394-018-1803-1","article-title":"LC\u2013MS\/MS Based 25(OH)D Status in a Large Southern European Outpatient Cohort: Gender- and Age-Specific Differences","volume":"58","author":"Giuliani","year":"2019","journal-title":"Eur. J. Nutr."}],"container-title":["Nutrients"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-6643\/17\/23\/3783\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,12,4]],"date-time":"2025-12-04T05:29:26Z","timestamp":1764826166000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-6643\/17\/23\/3783"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,12,2]]},"references-count":62,"journal-issue":{"issue":"23","published-online":{"date-parts":[[2025,12]]}},"alternative-id":["nu17233783"],"URL":"https:\/\/doi.org\/10.3390\/nu17233783","relation":{},"ISSN":["2072-6643"],"issn-type":[{"type":"electronic","value":"2072-6643"}],"subject":[],"published":{"date-parts":[[2025,12,2]]}}}