الفهرس 
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Abstract
ART has become widely applied nowadays with the dream of becoming a mother or a father for the infertile couple coming to real life due to advances in that field. IVF is still the most important technique. In the process of IVF, a sequence of highly coordinated steps is arranged. Embryo transfer can be considered the final determinant step.
Standardization of the procedures of embryo transfer has been paid great attention. The time frame from the thawing to loading can be critical and the optimal time interval is a matter of interest and thus our study has targeted this issue. Clinical pregnancy rate is considered the main outcome measure.
Our study aimed at assessment of the effect of the time interval passing from thawing to loading of frozen embryo into the catheter on the clinical pregnancy rate. It was a retrospective analysis, in which data from all frozen-thawed blastocyst or cleavage stage embryo transfer cycles meeting the inclusion criteria were collected from candidates attending the Assisted Reproduction Unit at Ain Shams University Maternity hospital. The study extended from the 1st of January 2015 through the 1st of January 2020. There were 976 patients who underwent 1092 frozen embryo transfer who met the inclusion criteria.
The thawing-loading interval was found to vary according to the routine practice of the setting. In the Reproductive Unit at the department of Obstetrics and Gynecology in the University Medical Centre of Ljubljana in Slovenia, the transfer is usually done 1 hour after the thawing. Another protocol in the division of Reproductive Sciences at the University of Toronto practices transfer at 2-4 hours after thawing. Thus it was a matter of interest to study the effect of the length of duration of time following thawing of the frozen embryo until the loading of the embryo into the catheter for transfer to find out the best time interval as regards the pregnancy outcome.
It was found that a thawing-loading interval between 60-239 minutes 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 was significantly associated with decreased probability of clinical pregnancy.
Our work has ended up with defining a time interval which was described to be associated with better pregnancy outcome. This time interval is estimated to be from two hours up to 4 hours, above which prolonged culture does not secure better outcome and below which the time interval is not enough for the embryo to regain its activity.
Further prospective cohort studies in that issue, as it is proved to have an impact on pregnancy outcome, are recommended with the aim of optimization of the thawing-loading interval instead of institutional variations based upon personal experience