Impact of Thawing-Loading Interval of Frozen Embryo on Pregnancy Outcome: Retrospective Analysis

Abstract

Background: Embryo transfer is a critical final step in the In Vitro fertilization (IVF) cycle. A great concern has been with standardization of the procedures of embryo transfer to improve outcome. The aim is to identify the impact of embryo thawing-loading interval (the time interval passing from thawing to loading of frozen embryo into the catheter) on pregnancy outcome. Results: The study was divided into quartiles according to thawing-loading interval in minutes (G I: <60; G II: 60–119; G III: 120–239; G IV: 240 and above). Numerical variables are presented as median and interquartile range and inter-group differences are compared using the Mann-Whitney test. Categorical variables are presented as numbers and percentages and differences are compared using the chi-squared test for trend. After adjustment for age of woman, time of previous failed ICSI trials, number and maturity of transferred embryos, a thawing-loading interval between 60-119 minutes (adjusted odds ratio = 2.222, 95% CI = 1.370 to 3.603, P- value = 0.001) or between 120-239 minutes (adjusted odds ratio = 1.924, 95% CI = 1.172 to 3.161, P- value = 0.010) was independently associated with increased probability of clinical pregnancy compared with a thawing-loading interval of <60 minutes. On the other hand, a thawing-loading interval of ≥240 minutes significantly decreased the probability of clinical pregnancy (adjusted odds ratio = 0.378, 95% CI 0.215 to 0.664, P- value = 0.001). Conclusion: After adjusting for potential confounders, this analysis found that a thawing-loading interval between 60-239 minutes was independently associated with better pregnancy outcomes compared with a thawing-loading interval of <60 minutes. On the other hand, a thawing-loading interval of ≥240 minutes was significantly associated with worse outcome.