The immediate postimplantation development of tetraploid mouse blastocysts.

The development during and immediately after the implantation period of 143 tetraploid blastocysts was studied both in vitro and in vivo; 58-7% in vitro and 38-8% in vivo were found to exhibit the changes associated with the early implanting blastocyst, i.e. giant cell transformation of the trophoblast and induction of the decidual cell reaction in the uterus. Of these 38-7% in vitro and 19-4% in vivo showed evidence of inner cell mass function during this time but only two in each system could be claimed as showing normal development. Examination of the developing blastocyst leads to the conclusion that lack of cell numbers in the inner cell mass is the most likely reason for the poor development of tetraploid embryos and suggests that the minimum number of ICM cells required to fulfil its role in embryogenesis is between four and eight.