[A comparative study of two-cell embryos of CBA and F1 mice in a human in vitro fertilization program]

The two-cell mouse embryo can develop in a chemically defined medium to the blastocyst stage but conditions must be strictly controlled. Fresh T6 (Whittingham's) medium is being used weekly for this purpose in our laboratory and subjected to a 5% CO2-in-air system 24 hours prior to use. Experiments were designed to determine whether two-cell embryos obtained from an F1 (CBA X C57/B1/6) X F1 cross were superior to the easily obtainable CBA X ICR cross. The aim was to get a 90% blastocyst result for use as a quality control. Eight experiments were performed over a 6-week period. The CBA two-cell embryos were compared with the F1 group under identical conditions. A total of 177 two-cell embryos were obtained from the CBA group and 214 two-cell embryos from the F1 group. In the CBA group 51 developed to the blastocyst stage (28.8%) compared with 187 in the F1 group (87.4%) (P less than 0.0001). In conclusion, it is advisable to obtain F1 mice to use weekly in the laboratory as a quality control measure. The CBA group yields poor cultures, and this leads to unnecessary laboratory confusion.