Pregnancy And Neonatal Outcomes After Long-term Vitrification Of Blastocysts Among 6900 Patients Following Their Last Live Birth

ObjectiveTo evaluate whether prolonged storage of vitrified blastocysts negatively impacts pregnancy and neonatal outcomes.MethodsRecords of all patients who underwent assisted reproductive technology(ART)treatment between January 2011 and January 2021 at the Center for Reproductive Medicine,Shandong University,were reviewed in the retrospective cohort study.A total of 6900 patients who desired to transfer their vitrified blastocysts from the same oocyte retrieval cycle as their last live birth were included in our study.Each patient was included only once.Patients who underwent embryo transfer during the embryo cleavage-stage,undertook preimplantation genetic testing(PGT),and experienced neonatal deaths after embryo transfer from the same oocyte retrieval cycle were excluded.Five storage duration groups were formed:1890 patients in group 1(storage duration<3 years),2693 patients in group 2(storage duration of 3-4 years),1344 patients in group 3(storage duration of 4-5 years),578 patients in group 4(storage duration of 5-6 years),and 395 patients in group 5(storage duration ≥6 years but ≤10.5 years).The primary outcomes in this study included the rates of blastocyst survival,biochemical pregnancy,clinical pregnancy,miscarriage,ectopic pregnancy,and live birth.The newborn’s sex and birth weight and the preterm rate were evaluated as the secondary outcomes.In addition,clinical and laboratory data that may affect pregnancy and neonatal outcomes were also compared among five groups,including maternal age at oocyte retrieval,maternal age at frozen embryo transfer(FET),body mass index(BMI),infertility duration,infertility causes,uterine morphology,number of previous oocyte retrieval cycles,fertilization method,number of basal follicles,number of oocytes retrieved,number of blastocysts vitrified,number of blastocysts transferred,blastocyst quality before vitrification,blastocyst quality at transfer,endometrial preparation program,and endometrial thickness.ResultsOf the 6,900 patients,71 patients canceled their transfer cycles owing to the failure of blastocyst recovery:16 patients in group 1,21 patients in group 2,15 patients in group 3,9 patients in group 4,and 10 patients in group 5.The survival rates of the vitrified blastocysts significantly decreased with prolonged storage from group 1 to the subsequent groups 2,3,4,and 5(group 1:93.51%,group 2:89.61%,group 3:81.68%,group 4:78.43%,group 5:75.27%;P<0.0001).The baseline characteristics and clinical outcomes of the 6829 patients with different embryo storage durations who underwent first vitrified-warmed blastocyst transfer after their last live birth were compared.No significant differences were noted among the five groups in terms of the maternal age at oocyte retrieval,body mass index,infertility duration,uterine morphology,fertilization methods,and number of previous oocyte retrieval cycles.The rates of biochemical pregnancy(group 1:69.32%,group 2:67.51%,group 3:66.14%,group 4:67.31%,group 5:57.66%),clinical pregnancy(group 1:62.75%,group 2:61.68%,group 3:60.12%,group 4:60.11%,group 5:50.13%),and live birth(group 1:52.77%,group 2;51.83%,group 3:49.13%,group 4:49.56%,group 4:40.78%)were significantly decreased when the vitrified blastocysts were stored for more than 6 years(group 5)compared with these for less than 3 years(group 1),but no distinct differences were found in these above-mentioned indicators among group 1,2,3,and group 4(group 1 as reference).However,no significant differences were noted in the rates of miscarriage and ectopic pregnancy and neonatal outcomes upon prolonged storage of vitrified blastocysts.After adjusting for potential confounding factors,the final results were consistent with those of the above-mentioned analyses.ConclusionTo summarize,our study revealed that long-term blastocyst vitrification for more than 6 years can negatively affect the rates of biochemical pregnancy,clinical pregnancy,and live birth.However,none of the other pregnancy and neonatal outcomes were negatively affected by the cryopreservation duration of vitrified blastocysts,and vitrified blastocysts stored for prolonged durations appeared to be a safe option for use in ARTs.