Vitrification of two-cell rat embryos derived from immature hypothyroid rdw rats by in vitro fertilization in ethylene glycol-based solutions.

Two-cell embryos derived from immature rdw rats by in vitro fertilization (IVF) were vitrified in ethylene glycol-based solutions. Embryos exposed to EFS20 before being vitrified in EFS40 exhibited improved viability in vitro. All embryos exposed to EFS20 for 1-3 min before vitrification in EFS40 were morphologically normal. However, 2-3 min of exposure to EFS20 increased the number of embryos that developed beyond the four-cell stage. More embryos exposed to EFS20 for 2-3 min developed to morulae (63-64%) and blastocysts (34-38%) than those exposed for 1 min (35 and 10%, respectively). After transfer, 33% of embryos exposed to EFS20 for 3 min and vitrified in EFS40 developed to term compared to 29% of fresh embryos. Fifteen (47%) of live young were homozygous rdw and all of the others were heterozygous rats. The present study demonstrated that vitrification in EFS solution can be routinely used to cryopreserve rat two-cell IVF-embryos with no loss of viability.