Risk Factors Of Monozygotic Twinning After Elective Single Blastocyst Transfer

Objective:To investigate the incidence and risk factors associated with monozygotic twinning(MZT)after elective single blastocyst transfer(eSBT).Methods:A total of 27595 cycles of elective single blastocyst transfer with clinical pregnancies in Reproductive Hospital Affiliated to Shandong University between January 2013 and January 2019 were retrospectively analyzed.3123 cycles of fresh blastosyst transfer were divided into monozygotic twin pregnancy group(n=83)and non-monozygotic pregnancy group(n=3040).24472 cycles of frozen-thawed blastocyst transfer were divided into MZT group(n=868)and non-MZT group(n=23604).If the fetal sac or fetal heart or fetal pole≥ 2 was judged as MZT pregnancy,SPSS statistics showed that it was statistically significant(P<0.05).Results:The MZT rate was 2.66%(83/3123)in fresh blastocyst transfer cycle and 3.55%(868/24472)in frozen-thawed blastocyst transfer cycle.No statistically significant differences were observed in parameters of fresh cycles between MZT and other non-MZT pregnancies after logistic regression analysis.The results of logistic regression analysis of frozen cycles showed that age,the number of high-quality embryos and the mode of assisted pregnancy had significant effects on the occurrence of MZT.With the increase of age(30.71±4.30 vs 31.11±4.40),the probability of MZT decreased.The incidence of MZT after IVF and ICSI was higher than the incidence after PGT(3.73%vs 2.00%;OR 1.94;95%CI 1.374-2.741).Conclusion:In the fresh blastocyst transfer cycle and frozen-thawed blastocyst transfer cycle,e twin pregnancy rate of young patients is higher,,such as younger age,lower basal FSH,lower amount of Gn initiation,and more high-quality embryos.This may be due to the fact that the eggs and embryos from young patients are more likely to be affected by ovulation induction and in vitro embryo culture.Compared with IVF and ICSI groups,the incidence of PGT group was lower than that of IVF and ICSI groups,which may be related to the younger age of IVF and ICSI patients,which also indicates that PGT embryo microsurgery does not increase the risk of MZT.