Michael, I don't believe that your argument of gastrulation as personhood as a sign of personhood is logical and holds any water.  If mind is part of soul, then we are talking around 22 weeks gestation.  Yet none of us know for sure what constitutes a human person with a soul.  However, if mind is not important than the simplest one celled animals might also have souls..   I suppose that is possible but then there is no importance to gastrulation at all.  Again I was taught by the good Sisters of Charity that mind IS indeed a subset of soul.  If, this is true, and I believe it is, then there is not a possibility of personhood until there is the development of an early functioning cerebral cortex.  This does not occur until about 22 weeks.  Yet if a fetus of 22 weeks threatens the life of a living mother, then it is her decision with the aid of her doctor to decide what to do.  Humans simply do not know when there is personhood or soul...