Background: Embryo transfer (ET) influences pregnancy rates in patients undergoing assisted reproduction. Data are conflicting as to which variables affect ET success. This study examines variables that may affect outcome after ET in assisted reproductive technology patients who had high-quality embryos transferred.

Methods: Over a 23 month period, 669 consecutive cycles were examined. Only patients having grade I and grade II embryos, or blastocyst transfers, were included in this retrospective analysis. A total of 584 consecutive cycles met study criteria. At the time of ET, the following variables were recorded: aborted first attempt at ET; presence of blood and/or mucus in or on the transfer catheter after ET; ease of ET as judged by provider; need for mock embryo transfer immediately before the actual transfer and retention of embryos in the transfer catheter. These variables were retrospectively analysed for their impact on implantation rate (IR) and clinical pregnancy rate (CPR).

Results: There were 290 gestations (49.7% CPR). Multiple attempts at ET, subjective difficulty of ET, performance of a sham pass immediately prior to embryo transfer, and presence of mucus on or in the catheter did not affect the CPR or IR. No difference was noted in the mean age of patients having or lacking any of these factors. There was a significant association between the presence of blood on or in the catheter and decreased IR (P = 0.015) and CPR (P = 0.004). Retained embryos also decreased IR (P = 0.03). Multivariable analysis confirmed that the presence of blood on the transfer catheter was the most important of these transfer characteristics in predicting IR (P = 0.042) and CPR (P = 0.018).

Conclusions: These results suggest that when only high-grade embryos or blastocysts are transferred, the presence of blood on the catheter is associated with decreased IR and CPR in assisted reproduction.