From Womb to World
The utter triviality of birth for the moral status of an emerging human being is a long-standing claim in academic discussion about abortion, as we are by now well aware. In one iteration of that view, LW Sumner categorically dismisses the relevance of birth to moral status in the following terms:
Birth is a shallow and arbitrary criterion of moral standing, and there seems to be no way of connecting it to a deeper account. In most respects, the infant shortly after birth has the 
same natural characteristics (is the same kind of creature) as a fetus shortly before birth; the same size, shape, internal constitution, species membership, capacities, level of consciousness and so forth. Biologically, a full-term infant resembles a fetus much more than it resembles a zygote or an embryo.  
Similarly, Jeff McMahan has challenged the moral distinction between infants and viable fetuses, questioning how the law can, with moral consistency, permit the abortion of fetuses at twenty weeks’ gestation but not the infanticide of babies born prematurely at the same gestational age.23 The problem of consistency, he claims, is raised by the fact that there is no ‘intrinsic’ difference between the two, only the ‘extrinsic’ difference of location. One manifestation of this inconsistency, he highlights, is that people will often accept the legitimacy of late abortion for reasons of fetal abnormality, like Down’s Syndrome, while balking at the very suggestion of infanticide for the same reasons.24
I have argued so far that there is a moral interest in specifying personhood as a range property, stemming from the necessity for what Ian Carter calls opacity respect. I have also pointed out that settling on a threshold into that range by means of stipulation can be a legal end in itself. As Endicott explains, all legal resolution by stipulation entails a certain kind of arbitrariness, in that there will be no principled reason to place the boundary-line where it is and not a fraction to either side. Thinking again about the kind of moral arbitrariness to which McMahan alludes, let us accept, for now, that there is no significant moral distinction between human beings of the same gestational age that are on either side of the vaginal canal. The legal interests in stipulation—practical resolution, and the elimination of other forms of arbitrariness, like unpredictability and the different treatment of like cases—are, however, unaffected by this. As Endicott says, the only questions one need ask about a candidate threshold are whether it falls within the range of acceptable boundary-lines and whether there is any decisive reason against placing the threshold there. The fact that no principled distinction can be drawn between full-term fetuses and neonates, if that is true, cannot count as such a reason, since that only implicates the kind of arbitrariness that goes hand in hand with stipulation at any point.
Still, one might hope to see reasons of at least some kind for stipulating birth as the threshold for legal personhood, namely, reasons to favour it over other thresholds within an acceptable margin. I think that reasons of this kind are in fact forthcoming. As I hope to illustrate, birth is a particularly appropriate minimum threshold for entry into personhood’s range for reasons having to do with the procedural interests in stipulation (certainty, consistency, and so on) and the essential preconditions for fully realized personhood.
-  ibid 8.
-  LW Sumner, Abortion and Moral Theory (Princeton University Press 1981) 53.
-  Jeff McMahan, ‘Infanticide and Moral Consistency’ (2013) 39 Journal of Medical Ethics 273.
-  24 For a simple restatement of this line of thought, see Alberto Giubilini and Francesca Minerva,‘After-Birth Abortion. Why Should the Baby Live?’ (2013) 39 Journal of Medical Ethics 261.