Factors Influencing Pregnancy Outcome Following Slow Cooling Cryoembryo Transfer and Risk of Multiple Conception

ObjectiveTo investigate the factors that influence the potential for cryoembryo implantation and multiple pregnancy.MethodsIn this retrospective study, a total of 937 thawing cycles (859 couples) in which 3286 d 3-embryos were thawed. Rates of implantation, clinical pregnancy and multiple conception following FET were observed.ResultsThere were significant differences in female age (P<0.05) and number of good quality embryos (P<0.05) between cycles that resulted in pregnancy and those did not. There was a trend toward decreasing rates of implantation, clinical pregnancy and multiple pregnancy with increasing female age. Compared with transferring 1 good quality embryo, clinical pregnancy rate of transferring 2 and 3 good quality embryos was increased significantly (P<0.001), there was no significant difference in clinical pregnancy rate between transferring 2 and 3 good quality embryos. Multiple pregnancy rate was increased significantly in the group of transferring 3 good quality embryos (P<0.05), but there was no significant differences in multiple pregnancy rate between transferring 1 and 2 good quality embryos. Younger women (≤ 30 years) also had a significantly higher multiple pregnancy rates (28.13%) than the older ones(>35 years) (13.64%). With an increase in age from ≤ 30 years to>40 years, clinical pregnancy rate declined from 45.61% to 25.00%.ConclusionFemale age and the number of good quality embryos transferred are important factors influencing the clinical and multiple pregnancy rate, reducing the number of good quality embryos transferred may decrease the rate of multiple pregnancy but do not affect the clinical pregnancy rate.