Transport of vitrified-warmed ICSI blastocysts in straws for up to 5 hours does not affect the pregnancy rate

Abstract

An increasing desire from embryo owners to have embryos transferred to their recipients at their private place, instead of bringing their recipient mare to the clinic for transfer, has led to this study, investigating whether the transport of embryos in straws, can be performed without affecting the pregnancy rate. The present study aimed to determine if vitrified-warmed ICSI blastocysts could be loaded in 0,25 ml straws in a buffered, commercial media (GMOPS Plus, Vitrolife, Sweden) and transported in a versatile shipping incubator (26237, WTA), at 38°C for up to 5 hours driving by car without affecting the pregnancy rate. Blastocysts were produced by conventional ICSI with oocytes recovered from immature follicles by transvaginal ultrasound-guided oocyte pick up in a clinical commercial program in Denmark. This study was performed in the transfer season 2021 (March to August) and included 90 embryos from different breeds, mainly Warmblood mares. The blastocysts were vitrified on days 7-10 after ICSI using commercial vitrification media (VitriFreeze, FertiPro, Belgium), and an open vitrification device (VitriFit, CooperSurgical, Denmark). On the day before the transfer, blastocysts were warmed in commercial warming media (VitriThaw, FertiPro) and incubated overnight in EQ-IVC2 (IVF Bioscience, UK), 6% CO2, 38.2°C. On the day of transfer, embryos going to be transferred at the client's place were loaded in 0,25 ml straws with warm GMOPS Plus and placed in the WTA shipping incubator at 38°C. All embryos were transferred by manual and transcervical method to recipient mares being 4 to 5days after ovulation. In total 90 embryos were transferred; 39 embryos were transported in straws and 51 embryos were transferred directly at the clinic, and no significant difference in the pregnancy rate was observed between transported embryos (26/39, 67%) and directly transferred embryos (33/51, 65%) 7-10 days after transfer. When checking for the heartbeat (∼day 30 after ovulation), also no significant difference in the heartbeat pregnancy rate was observed between the transported embryos (24/39, 62%) and directly transferred embryos (29/51, 57%). In conclusion, these data show that equine ICSI blastocysts can be transported in straws at 38°C for up to 5 hours by car in a commercial medium, without affecting the heartbeat pregnancy rate. For future studies, it would be interesting to investigate if vitrified-warmed ICSI blastocysts can be transported in straws for more than 5 hours without affecting the pregnancy rate.