biostudies-literature00470Unknown12Li D<h4>Objective</h4>To evaluate the clinical effect of mild stimulation with letrozole on pregnancy outcomes in ovulatory women undergoing frozen embryo transfer (FET) compared to natural cycle.<h4>Design</h4>Retrospective observational study.<h4>Setting</h4>Tertiary care academic medical center.<h4>Population</h4>A total of 6,874 infertile women with regular menstrual cycles (21-35 days) met the criteria for this study in the period from 2013 to 2020.<h4>Methods</h4>All patients who were prepared for and underwent FET were divided into two groups: a modified natural cycle (NC) group (n=3,958) and a letrozole cycle group (n=2,916).<h4>Main outcome measures</h4>The primary outcome of the study was clinical pregnancy rate. Secondary outcome measures were endometrial thickness, rates of implantation, positive HCG test, live birth, early miscarriage and ectopic pregnancy.<h4>Results</h4>The clinical pregnancy rate was not statistically different between the modified NC-FET group and the letrozole-FFT group before (crude OR 0.99, 95% CI 0.90-1.09, P=0.902>0.05) and after propensity score matching (PSM) (crude OR 1.01, 95% CI 0.91-1.12, P=0.870>0.05). After multivariable logistic regression analysis, the clinical pregnancy rate remained insignificant before (adjusted OR 1.00, 95% CI 0.91-1.10, P=0.979>0.05) and after matching (adjusted OR 1.00, 95% CI 0.89-1.11, P=0.936>0.05), respectively. Similarly, in the crude and adjusted analysis, the positive HCG test, implantation, live birth and early miscarriage rates were also comparable in the letrozole-FFT group and modified NC-FET group before and after matching. Furthermore, the endometrial thickness of letrozole-FFT group was similar to that of modified NC-FET group with adjusted analysis.<h4>Conclusion</h4>Our observation suggests that mild stimulation with letrozole could produce similar pregnancy outcomes in ovulatory patients who undergo FET when compared with a natural cycle.Frontiers in endocrinology677689https://www.ebi.ac.uk/biostudies/studies/S-EPMC8493067biostudies-literatureFrozen Embryo Transfer in Mildly Stimulated Cycle With Letrozole Compared to Natural Cycle in Ovulatory Women: A Large Retrospective Study.PMC8493067Cai RChen QLi DHuang JLu XKhor SKuang YLyu Q47falseFrozen Embryo Transfer in Mildly Stimulated Cycle With Letrozole Compared to Natural Cycle in Ovulatory Women: A Large Retrospective Study.<h4>Objective</h4>To evaluate the clinical effect of mild stimulation with letrozole on pregnancy outcomes in ovulatory women undergoing frozen embryo transfer (FET) compared to natural cycle.<h4>Design</h4>Retrospective observational study.<h4>Setting</h4>Tertiary care academic medical center.<h4>Population</h4>A total of 6,874 infertile women with regular menstrual cycles (21-35 days) met the criteria for this study in the period from 2013 to 2020.<h4>Methods</h4>All patients who were prepared for and underwent FET were divided into two groups: a modified natural cycle (NC) group (n=3,958) and a letrozole cycle group (n=2,916).<h4>Main outcome measures</h4>The primary outcome of the study was clinical pregnancy rate. Secondary outcome measures were endometrial thickness, rates of implantation, positive HCG test, live birth, early miscarriage and ectopic pregnancy.<h4>Results</h4>The clinical pregnancy rate was not statistically different between the modified NC-FET group and the letrozole-FFT group before (crude OR 0.99, 95% CI 0.90-1.09, P=0.902>0.05) and after propensity score matching (PSM) (crude OR 1.01, 95% CI 0.91-1.12, P=0.870>0.05). After multivariable logistic regression analysis, the clinical pregnancy rate remained insignificant before (adjusted OR 1.00, 95% CI 0.91-1.10, P=0.979>0.05) and after matching (adjusted OR 1.00, 95% CI 0.89-1.11, P=0.936>0.05), respectively. Similarly, in the crude and adjusted analysis, the positive HCG test, implantation, live birth and early miscarriage rates were also comparable in the letrozole-FFT group and modified NC-FET group before and after matching. Furthermore, the endometrial thickness of letrozole-FFT group was similar to that of modified NC-FET group with adjusted analysis.<h4>Conclusion</h4>Our observation suggests that mild stimulation with letrozole could produce similar pregnancy outcomes in ovulatory patients who undergo FET when compared with a natural cycle.2021-01-01T00:00:00Z20212024-02-15T17:31:06.788Z2022-02-11T12:00:53.663ZS-EPMC84930673463031810.3389/fendo.2021.677689