Every second counts: the association of embryo transfer duration with live birth following 2267 single, euploid, frozen embryo transfer.

Purpose: To identify the impact of the duration of the embryo transfer procedure on pregnancy outcomes.

Methods: This was a retrospective cohort study at a single center including single euploid frozen embryo transfers from April to December 2022. Embryo transfer time was defined as the total time (seconds) from when the embryologist handed the catheter with the loaded embryo to the physician, to the release of the embryo into the uterus. Time measurements were divided into quartiles: (1) 4-27 s, (2) 28-38 s, (3) 39-54 s, and (4) 55-1028 s. The primary outcome was the probability of live birth per transfer. Secondary outcomes included biochemical pregnancy, clinical pregnancy, and pregnancy loss.

Results: A total of 2267 frozen embryo transfer cycles were included in the analysis. The overall live birth rate was 59.8% (1356/2267). Compared to the fastest time (1st quartile), the probability of live birth was significantly decreased for couples with the longest transfer times (4th quartile) after adjusting for possible confounding variables (aOR, 0.76; 95% CI 0.58-0.99; p = 0.046). When patients with more difficult embryo transfers, that as a result may be inherently longer, were excluded, the results were the same as the primary model. However, when data was analyzed using only first transfers, compared to the shortest transfer time quartile (1st), there was a significant decreased probability of live birth in the 3rd quartile (OR 0.63, 95% CI 0.41-0.94, p = 0.025), but no significant differences in the 2nd or 4th quartile groups (p = 0.213, p = 0.800). There were no differences in the probability of biochemical pregnancy, clinical pregnancy, or pregnancy loss in the fully adjusted model.

Conclusion: The longest embryo transfer times are associated with significantly decreased probability of live birth.