unlike mural trophectoderm cells which stop proliferating and become large polyploid cells (the primary trophoblastic giant cells) by endoreduplication, polar trophectoderm cells remain diploid, continue to proliferate and give rise to both the ectoplacental cone and the extraembryonic ectoderm[MP]

The part of the trophectoderm overlying the inner cell mass. [See_Kaufman_MH_and_Bard_JBL, The_anatomical_basis_of_mouse_development_(1999)_San_Diego:_Academic_Press, p.10][VHOG]

uberon

polar trophoblast

(...) the trophoblast develops rapidly so that contact may be made with the maternal uterine tissues when conditions are appropriate. We have here an excellent example of an embryonic adaptation, the development of a structure never present in either adult or embryo of 'lower' vertebrates.[well established][VHOG]

UBERON:0006280