The fate of trophoblast retained within the oviduct in the mouse.

Pre-implantation blastocysts or trophoblast, obtained from ectoplacental cones, were transferred to the right oviducts of both pregnant and nonpregnant mice. Blastocysts which remained within the oviductal lumen did not show evidence of further differentiation into trophoblast although they readily implanted on various extratubal sites. Similarly, trophoblast from ectoplacental cones failed to show invasive properties when restricted to the lumen. In 3 cases where trophoblast giant cells were found within the tubal lumen, entry appeared to have been contingent on an existing breach in the epithelium. Invasive action on tubal epithelium by trophoblast was not seen.