Comparison of pregnancy outcomes in young patients following fresh versus frozen single blastocyst transfer:A retrospective study

Abstract Background：Previous studies have shown that, in young women, single blastocyst transfer can achieve satisfactory pregnancy results; however, few studies exist regarding the difference between fresh and frozen-thawed single blastocyst transfer. To provide further clinical strategies for single blastocyst transfer, the purpose of this retrospective analysis was to compare the pregnancy outcomes of young patients who received fresh or frozen-thawed single blastocyst transfer.Methods: A retrospective analysis of patients, aged ≤35 years, who underwent single blastocyst transfer was conducted from January 2018 to December 2018 in the reproductive center of the Second Affiliated Hospital of Wenzhou Medical University (Wenzhou, China). In total, 901 patients were included and were divided into two groups, based on the type of transfer cycle: the fresh embryo transfer cycle group (group A; n=693) and the frozen-thawed embryo transfer cycle group (group B; n=208). The laboratory and pregnancy outcomes were compared between the groups.Results：The number of oocytes retrieved in group B was significantly higher than in group A (P＜0.05). The early miscarriage rate in group B was significantly higher than in group A and was significantly different (P＜0.05). Frozen-thawed single blastocyst transplantation was an independent risk factor for early miscarriage. Other basic conditions and obstetric pregnancy outcomes were not significantly different between the two groups.Conclusions：Favourable pregnancy outcomes could be obtained with fresh and frozen-thawed single blastocyst transfer in young patients. However, because the early miscarriage rate was higher in the frozen-thawed embryo transfer group, further research is needed to determine the cause and possible solutions.