Universal warming protocol” for a transnational egg donation program with vitrified oocytes: a retrospective multi-centre study

Abstract

We have previously demonstrated that it is possible to warm vitrified human oocytes using a “universal warming protocol” based on subsequent steps with 1M and 0.5 M of ECCP regardless of the warming kit brand; this study investigated the clinical efficiency of this protocol on shipped oocytes in a transnational donor program. Retrospective multi-center observational study on a cohort of 238 patients enrolled in egg donation programs from 02 March 2017 to 19 September 2018. Primary endpoint was the survival rate (n° oocytes surviving/ n° oocytes warmed). Secondary endpoints were fertilization rate (n° fertilized oocytes / n° injected oocytes), blastulation rate (n°blastocysts obtained / n° fertilized oocytes), implantation rate (n°implanted embryos / n° of transferred embryos) and live birth rate (n° of pregnancies giving births /n° of embryo transfer). Donated oocytes vitrified in Spain, warmed in 2 centers in Italy where ICSI and embryo transfer (ET) were performed. Number of oocytes 1898, ET 238. Vitrification with Vitrification Kit (Kitazato, Japan); warming with two different kits: Kitazato Warming Kit and Vit Kit®-Thaw (Irvine-Fujifilm, US). Warmed oocytes assigned to 2 groups: KK (Kitazato/Kitazato) 939, and KI (Kitazato/Irvine-Fujifilm) 959. Vitrification with Cryotop (Kitazato); embryo culture with Embryoscope (Vitrolife, Sweden). ET at blastocyst stage. Mean age of donors and recipients was comparable. Survival, fertilization, blastulation and implantation rates were all statistically comparable between the study groups. Survival rate was 84.6% (795/939) in group KK vs 82.1% (787/959) in group KI. Fertilization rate was 75.7% (602/795) vs 80.4% (633/787), and blastulation rate 58.5% (352/602) vs 57.8% (366/633). Implantation rate was 38.3 % (80/209) in group KK vs 45.9% (84/183) in group KI. Live birth rate was 52.5% (62/118) in KK and 45.0% (54/120) in KI. The proven clinical efficiency of this “universal warming protocol” with ready-to-use warming kits with 1 and 0.5 M of ECCP simplifies vitrified oocyte exchange between AR centers in different countries, overcoming potential regulatory/commercial/availability differences affecting clinical practice.