Live birth rate and neonatal outcome following cleavage-stage embryo transfer versus blastocyst transfer using the freeze-all strategy

Research question: What are the live birth rates and neonatal outcomes following cleavage-stage embryo transfer and blastocyst transfer in a freeze-all treatment scenario? Design: This was a retrospective cohort study. All good-quality embryos were frozen on the third day; the remaining embryos were grown on until they reached blastocyst stage and then frozen. Between 2007 and 2016, 11,801 patients underwent cleavage-stage embryo transfer and 1009 patients underwent blastocyst transfer in the first treatment cycle using the freeze-all strategy. The live birth rate and neonatal outcomes were evaluated. Results: The live birth rate in the first frozen embryo transfer cycle was higher following blastocyst transfer than following cleavage-stage transfer (69.1% versus 55.5%, P < 0.01), but there was no difference in live birth rate in the second frozen embryo transfer cycle between blastocyst transfer and cleavage-stage transfer (45.2% versus 52.7%, P > 0.05). Similarly, no difference was found in the cumulative live birth rate for the first complete IVF cycle (71.1% versus 69.2%, P > 0.05). Blastocyst transfer gave a higher risk of preterm singleton delivery than did cleavage-stage transfer. However, there was no difference in the risk of early preterm delivery, low birth weight, very low birth weight, high birth weight and very high birth weight between the two groups. Conclusions: There is no evidence to support the superiority of blastocyst transfer compared with cleavage-stage transfer in a freeze-all treatment scenario. There may be a higher risk of preterm singleton delivery following blastocyst transfer than following cleavage-stage transfer but further studies are needed to verify this.