Implantation and Development of Mouse Eggs Transferred to the Uteri of Non-Progestational Mice

Summary. Four-day-old mouse embryos were transferred to the uterine lumen of virgin cyclic and ovariectomized mice; the eggs 'implanted' and developed only in mice whose endometrium was previously traumatized with a glass scraper. The histology of the mechanically induced implantation sites is described and similarities to normal implantation sites are discussed. Implanted embryos developed only to stages equivalent to 5 to 9 days of normal pregnancy, but the trophoblast continued to proliferate and invaded the endometrium, eroding maternal blood vessels and distending the uterus. In five of eight ovariectomized mice, plaques of decidual-like cells were found near the trophoblast 7 to 12 days after transfer.