{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,16]],"date-time":"2026-03-16T19:21:37Z","timestamp":1773688897627,"version":"3.50.1"},"reference-count":18,"publisher":"MDPI AG","issue":"13","license":[{"start":{"date-parts":[[2025,6,28]],"date-time":"2025-06-28T00:00:00Z","timestamp":1751068800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JCM"],"abstract":"<jats:p>Objective: Most studies concentrate on comparisons between the cleavage stage and blastocyst stage of embryos during in vitro stimulation treatment. We aimed, in this study, to compare the pregnancy rates of day 4 or day 5 blastocyst transfers, all derived from fresh, antagonist-regulated in vitro fertilization (IVF) cycles, and to evaluate the factors affecting pregnancy success. Methods: This retrospective cohort study evaluated 3681 fresh embryo transfer cycles conducted at a private IVF center between 2019 and 2021. Patients were divided into two groups based on the day of embryo transfer: day 4 (Group 1) and day 5 (Group 2). Subgroup analyses were performed according to age (\u226440 vs. &gt;40 years) and the number of oocytes retrieved (\u22644 vs. &gt;4). All patients underwent ovarian stimulation with FSH alone or in combination with hMG, and GnRH antagonist protocols were used for pituitary suppression. Final oocyte maturation was triggered with recombinant hCG, and fertilization was achieved via intracytoplasmic sperm injection (ICSI) for all cases. Embryos were cultured in sequential media and assessed daily until transfer on day 4 or day 5, based on embryo morphology and clinic logistics. Results: Pregnancy was more likely among women under 40 than among women over 40. There were a total of 1217 women who underwent day 4 transfer and 2464 women who underwent day 5 transfer. A total of 660 (54.2%) of the women transferred on day 4 developed pregnancy. Among those transferred on day 5, 1610 (65.3%) developed pregnancy. When compared to the 4th day, a single embryo transfer on the 5th day enhances pregnancy success by 1.8 times, while two embryo transfers raise it by 1.6 times. Furthermore, when the number of oocytes is greater than four and the number of embryos transferred is two, the pregnancy success rate is 2.5 times higher when embryo transfer is performed on the fifth day versus the fourth day. Regardless of age, oocyte count, or number of embryos transferred, 5th-day fresh embryo transfers enhanced pregnancy success by 1.9 times compared to 4th-day transfer. Conclusions: Transfers of fresh embryos on day 5 are superior to those on day 4 and should be favored, especially for people over the age of 40, regardless of the number of embryos transferred, even if that individual has fewer than four oocytes.<\/jats:p>","DOI":"10.3390\/jcm14134596","type":"journal-article","created":{"date-parts":[[2025,6,30]],"date-time":"2025-06-30T13:06:17Z","timestamp":1751288777000},"page":"4596","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Day 4 Versus Day 5 Fresh Embryo Transfer in In Vitro Fertilization: Is It All About Timing?"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2895-575X","authenticated-orcid":false,"given":"Alper","family":"\u015ei\u015fmano\u011flu","sequence":"first","affiliation":[{"name":"Department of Obstetrics and Gynecology, Alt\u0131nba\u015f University Faculty of Medicine, 34147 Istanbul, T\u00fcrkiye"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7634-3008","authenticated-orcid":false,"given":"S\u00fcleyman Cemil","family":"O\u011flak","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Health Sciences University, Gazi Ya\u015fargil Training and Research Hospital, 21500 Diyarbak\u0131r, T\u00fcrkiye"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Cenk","family":"\u00d6zcan","sequence":"additional","affiliation":[{"name":"Department of Embryology, Ota & Jinemed Hospital IVF Center, 34357 Istanbul, T\u00fcrkiye"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4718-6020","authenticated-orcid":false,"given":"Ulun","family":"Ulu\u011f","sequence":"additional","affiliation":[{"name":"Department of Obstetrics and Gynecology, Hali\u00e7 University Faculty of Medicine, 34060 Istanbul, T\u00fcrkiye"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,28]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"133","DOI":"10.1016\/j.rbmo.2018.12.001","article-title":"Towards the global coverage of a unified registry of IVF outcomes","volume":"38","author":"Fauser","year":"2019","journal-title":"Reprod. Biomed. Online"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"2368773","DOI":"10.1080\/01443615.2024.2368773","article-title":"Prognostic value of miR-223 for pregnancy outcomes in patients with in vitro fertilisation and intracytoplasmic sperm injection","volume":"44","author":"Song","year":"2024","journal-title":"J. Obstet. Gynaecol."},{"key":"ref_3","first-page":"348","article-title":"Association of ovarian stimulation and embryonic aneuploidy in in vitro fertilization cycles with preimplantation genetic testing: A narrative systematic review","volume":"26","year":"2022","journal-title":"JBRA Assist. Reprod."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"775","DOI":"10.1080\/09513590.2021.1939297","article-title":"Time, time, time: See what governs the luteal phase endocrinology","volume":"37","author":"Kol","year":"2021","journal-title":"Gynecol. 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Health"}],"container-title":["Journal of Clinical Medicine"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2077-0383\/14\/13\/4596\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T18:01:01Z","timestamp":1760032861000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2077-0383\/14\/13\/4596"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,6,28]]},"references-count":18,"journal-issue":{"issue":"13","published-online":{"date-parts":[[2025,7]]}},"alternative-id":["jcm14134596"],"URL":"https:\/\/doi.org\/10.3390\/jcm14134596","relation":{},"ISSN":["2077-0383"],"issn-type":[{"value":"2077-0383","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,6,28]]}}}