Study Of Pregnancy Outcomes Between Fresh And Frozen Embryo Transfer In Patients With Thin Endometrium On HCG Trigger Day

BackgroundThere are many factors that affect the pregnancy outcome of in vitro fertilization-embryo transfer(IVF-ET),including embryo quality,transfer method,endometrial receptivity(ER)and so on.Among them,endometrial thickness(EMT)is one of the important indicators of endometrial receptivity.At present,the definition of thin endometrium is still inconclusive,but the thinner endometrium thickness often suggests that we may get an unsatisfactory pregnancy outcome,which is one of the more difficult problems faced in the process of embryo transfer.However,there are no clear and effective measures to increase the thickness of the intima through drugs or other treatments to further improve the pregnancy outcome.Freeze-thaw embryo transfer is one of the important methods in assisted reproductive technology.It can effectively reduce the stimulation of a large number of gonadotropins and reduce the adverse effects of ovulation induction on endometrial receptivity.With the development and progress of freezing and thawing embryo technology,the freezing of whole embryos has been fully developed.For patients with thin endometrium found in the process of ovulation induction,whether we should choose to continue fresh embryo transfer is a question to be explored in clinical work.ObjectiveTo compare pregnancy outcomes between fresh and frozen embryo transfer in patients with thin endometrial thickness(EMT<7mm)on hCG trigger day,and to explore more favorable embryo transfer strategies.MethodsWe retrospectively analyzed a total of 769 patients with thin endometrial thickness on hCG trigger day who underwent embryo transfer with the first cycle of in vitro fertilization(IVF)or intracytoplasmic sperm injection(ICSI)treatment in our hospital from January 2016 to December 2018.According to transferred embryos whether or not be frozen,all patients were divided into two groups:fresh embryo transfer group(ET group)and frozen embryo transfer group(FET group).Propensity score-matched(PSM)was used to balance the influence of intergroup confounding factors and we finally counted ET group(n1=206)and FET group(n2=206)after matching.We compared the differences in the thickness of endometrial transformation days and in pregnancy outcomes between the two groups.They were further divided into 6mm<EMT≤7mm subgroup(268 cases)and EMT≤6mm subgroup(144 cases).The differences in pregnancy outcomes were compared between ET and FET.The endometrial thickness changes and pregnancy outcomes were further analyzed in the three endometrial preparation protocols of FET group.ResultsAfter matching by PSM,there was no significant difference in baseline characters between ET and FET groups.The EMT(6.5[6.0,7.0]vs7.0[6.5,8.0],P<0.001)and clinical pregnancy rates(32.5%vs45.6%,P<0.01)of FET group were significantly higher than those of ET group.Although the live birth rate was also higher than that in ET group,the difference was not statistically significant(26.7%vs33.0%,P>0.05).Further subgroup analysis showed that the EMT of FET group was significantly higher than that of ET group(P<0.01)in two subgroups;among them,the clinical pregnancy rate(CPR)and live birth rate(LBR)of FET group in the 6mm<EMT≤7mm subgroup were significantly higher than those of ET group(CPR:34.1%vs 54.9%,LBR:27.4%vs 39.8%,P<0.05);but there was no significant difference in CPR and LBR between FET group and ET group in the EMT≤6mm subgroup(CPR:29.6%vs28.8%,LBR:25.4%vs20.5%,P>0.05),although the EMT was improved during the frozen embryo transfer.The endometrial thickness of the three endometrial preparation protocols in FET group was thicker than that on the hCG trigger day.There were no significant differences in the endometrial improvement rate,clinical pregnancy rate and live birth rate among the three groups.However,the Clinical pregnancy loss rate of Minimal ovarian stimulation cycles is significantly higher than that of natural cycles and programmed cycles.ConclusionIn general,the EMT of patients with thin endometrium during the frozen embryo transfer cycle is higher than that of the hCG trigger day during COH.Patients with thin endometrium on hCG trigger day can obtain a higher clinical pregnancy rate in FET.Among them,those with 6mm<EMT≤7mm benefited more from frozen embryo transfer because of the significantly increased live birth rate;however,frozen embryo transfer for EMT≤6mm did not improve the clinical pregnancy rate and live birth rate,so fresh embryo transfer can also be chosen.