P –159 Slow-growing embryos should be frozen on day 5

AbstractStudy questionWhat is the live birth rate after frozen embryo transfer (FET) of slow-growing embryos frozen on day 5 (D5) or on day 6 (D6)?Summary answerThe live birth rate after single FET is significantly higher for slow-growing embryos frozen on D5 compared to those frozen on D6.What is known alreadyMost data on the outcomes of blastocyst transfer stem from studies that evaluate fresh transfer from normal growing D5 blastocyst ET. However not all embryos will begin blastulation nor reach the fully expanded stage by D5; those are the slow-growing embryos. Studies that compare D5 to D6 embryos in FET cycles show contradictory results. Some have reported higher clinical pregnancy rates after D5 FET, while others have reported similar outcomes for D5 and D6 cryopreserved blastocyst transfers. There is a lack of evidence regarding the best approach for vitrifying embryos that exhibit a slow developmental kinetic.Study design, size, durationThis retrospective cohort study included 821 single FET of slow-growing embryos frozen on D5 or D6, belonging to patients undergoing in vitro fertilization with donor oocytes between January 2011 and October 2019, in a single fertility center. The origin of blastocysts was either supernumerary embryos after fresh embryo transfer or blastocysts from freeze-all cycles. All embryos were transferred 2- 4h after thawing.Participants/materials, setting, methodsWe compared reproductive outcomes of slow-growing embryos frozen on D5 versus (n ...
Source: Human Reproduction - Category: Reproduction Medicine Source Type: research