I don't know what you mean by "no further" legal definitions.     The definitions we now have are perfect?  Or do  you mean there should be no legal definitions at all as to when personhood begins?

It's important to understand that these reproductive issues will never exist in a legal vacuum.   That is, there are contingents who are ever pushing to legally diminish the definition of when personhood begins.   That being so, there will always be conflict between the pro life and pro choice camps.