Developmental precocity after asynchronous egg transfer in mice.

Asynchronously transferred ova were found to implant 6-8 h earlier than did non-transferred eggs, indicating that the endometrium was receptive to implantation several hours before the native blastocysts were prepared to implant. This developmental precocity was also preserved on day 14, according to the results of a morphological rating study on day 14. Synchronously transferred ova showed no such developmental precocity. No statistically significant difference in implantation time or development on day 14 was found between the two strains, CBA and A/Jax. The importance of precocious development for planning teratological studies is emphasized.