Difficult embryo transfer (ET) components and cycle outcome. Which is more harmful?

Objective: To compare the impact of individual elements of difficult embryo transfer (D-ET): cervical traction (Cx-Tr), blood on outer sheath (Bl-OS), blood on transfer catheter (Bl-TC) and sounding (Snd) individually and in combination on clinical pregnancy rate (CPR) and implantation rates (IR) of ICSI cycles. Methods: A retrospective cohort study included 744 ICSI cycles. Easy embryo transfer (E-ET) was diagnosed if no resistance on passing the preloaded TC and the sheath through the cervix. Difficult transfer was defined if Cx-Tr and/or Snd was needed, and Bl-OS or Bl-TC was present. Cycle outcome was compared for E-ET and D-ET as a whole and individually with subgroups using Odds Ratio and 95% CI. Results: CPR for E-ET (45.6%) and D-ET (39.8%) is not statistically significantly different. Comparing E-ET with Cx-Tr, Bl-OS or Bl-TC, Snd showed significantly lower CPR with Bl-TC and Snd subgroups only. Although IR showed no significant difference between E-ET and over all components of D-ET it tended to be lower for Bl-TC and Snd subgroups. Conclusion: Cx-Tr and/or Bl-OS do not compromise CPR or IR. Only when Bl-TC and/or Snd the uterus at the time of ET is the CPR significantly undermined and IR tends to be impaired.