Impact of transfer time on pregnancy outcomes in frozen-embryo transfer cycles

In a highly controlled uterine environment, longer embryo transfer times did not negatively affect clinical pregnancy, implantation, or live birth rates in frozen- thawed blastocyst transfers.

Volume 109, Issue 3, Pages 467–472


Malinda S. Lee, M.D., M.B.A., Eden R. Cardozo, M.D., Anatte E. Karmon, M.D., Diane L. Wright, Ph.D., Thomas L. Toth, M.D.



To identify the impact of embryo transfer time (total seconds from the loading of the transfer catheter to the expulsion of the embryo(s) into the uterine cavity) on clinical pregnancy (CPR), implantation (IR), and live birth (LBR) rates.


Retrospective cohort study.


Academic hospital practice.


A total of 465 women undergoing 571 frozen-embryo transfers with the use of cryopreserved blastocysts in a single academic institution from 2007 through 2014.



Main Outcome Measure(s)

CPR, IR, and LBR.


The cohort was divided into tertiles according to transfer time in seconds (T1: 33–55; T2: 57–81; T3: 82–582) with mean (SD) transfer times of 47.4 (5.7), 67.1 (7.3), and 121.9 (55.1) seconds, respectively. Crude CPRs were 43.9%, 48.7%, and 48.7% among the respective tertiles, crude IRs were 36.9%, 39.9%, and 38.6%, and crude LBRs were 34.8%, 39.6%, and 36.0%. In univariate analysis, inferior cohort score, blood inside catheter, difficult mock transfer, and use of an outer sheath were negatively associated with CPR. No association was seen between physician performing the transfer (including fellows) and CPR. In multivariate regression, longer transfer time was not associated with CPR. With T1 as reference, adjusted odds ratios (95% confidence interval) were 1.28 (0.77–2.11) and 1.52 (0.85–2.71) for transfer time groups T2 and T3, respectively.


After adjusting for potential confounders, this analysis found that contrary to commonly held belief, longer embryo transfer times do not negatively affect CPR, IR, or LBR.

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Go to the profile of Micah J Hill
over 4 years ago

Thank you for the very interesting article and I look forward to the Journal Club Global this week!  The study findings are reassuring regarding transfer time not effecting pregnancy rates.  Im curious if the you look at just the very extremes of transfer times beyond the tertiles or 120 second time frame, if you see any drop in pregnancy rate?  There may not be power to statistically detect it with such few cases at the extremes, but I am curious.  Also, do you have a theory on why the use of an outer catheter was associated with lower pregnancy?  We use afterload technique for all our transfers.