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To compare the differences in pregnancy outcomes, the D4 and D5 groups were further divided into groups A and B based on single and double embryo transfers. Furthermore, the cohort was divided into two groups: those with live births (1116 cases) and those without (847 cases), enabling a deeper evaluation of the effects of D4 or D5 transplantation on assisted reproductive outcomes.<\/jats:p>\n              <\/jats:sec><jats:sec>\n                <jats:title>Results<\/jats:title>\n                <jats:p>In single embryo transfer, there was no significant difference between groups D4A and D5A (<jats:italic>P<\/jats:italic>\u2009&gt;\u20090.05). In double embryo transfer, group D4B had a lower newborn birthweight and a larger proportion of low birthweight infants (<jats:italic>P<\/jats:italic>\u2009&lt;\u20090.05). The preterm delivery rate, twin delivery rate, cesarean delivery rate, and percentage of low birthweight infants were lower in the D5A group than in the D5B group (<jats:italic>P<\/jats:italic>\u2009&lt;\u20090.05). Analysis of factors influencing live birth outcomes further confirmed the absence of a significant difference between D4 and D5 transplantation in achieving live birth (<jats:italic>P<\/jats:italic>\u2009&gt;\u20090.05).<\/jats:p>\n              <\/jats:sec><jats:sec>\n                <jats:title>Conclusion<\/jats:title>\n                <jats:p>When factors such as working life and hospital holidays are being considered, D4 morula transfer may be a good alternative to D5 blastocyst transfer. Given the in vitro fertilization\/intracytoplasmic sperm injection (IVF\/ICSI) success rate and risk of twin pregnancy, D4 morula transfer requires an adapted decision between single and double embryo transfer, although a single blastocyst transfer is recommended for the D5 transfer in order to decrease the twin pregnancy rate. In addition, age, endometrial thickness and other factors need to be taken into account to personalize the IVF program and optimize pregnancy outcomes.<\/jats:p>\n              <\/jats:sec>","DOI":"10.1186\/s12884-024-06597-7","type":"journal-article","created":{"date-parts":[[2024,7,3]],"date-time":"2024-07-03T14:13:50Z","timestamp":1720016030000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Comparison of pregnancy outcomes between 4th day morula and 5th day blastocyst after embryo transfer: a retrospective cohort study"],"prefix":"10.1186","volume":"24","author":[{"given":"Yiqun","family":"Sun","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Qi","family":"Shen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Haitao","family":"Xi","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Liucai","family":"Sui","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yanghua","family":"Fu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Junzhao","family":"Zhao","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2024,7,3]]},"reference":[{"issue":"4","key":"6597_CR1","doi-asserted-by":"publisher","first-page":"367","DOI":"10.1093\/humupd\/3.4.367","volume":"3","author":"DK Gardner","year":"1997","unstructured":"Gardner DK, Lane M. 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