I know this is not exactly your point, but it's important to remember that it's not exactly everything. The intra-uterine environment has a serious contribution to your development, and almost certainly transplanting the fecundated cell into a different mother would lead to a different person being born. Especially when it comes to things like intestinal flora, which mostly seems to get "seeded" from the mother during birth. Even the milk you ingest after birth significantly influences certain aspects of your basic biology (mostly the immune system).