That’s the thing: there is no clear cut line of demarcation. There will never be unanimous consensus. Which for me means: it has to be up to the mother and doctor .
There may not be a perfect bright line with unanimity… because people like LD and Jarhyn seem to think that personhood is magically conferred by delivery.
But I think the overwhelming majority of people would agree that a week prior to delivery falls clearly on the ‘baby’ side, and a reasonable majority would agree that a week after conception does not. I think it’s entirely plausible and reasonable to pick the inflection point, and maybe add a week to it. So if inflection is 28 weeks, set the voluntary limit at 29.
Don’t make a lack of perfection be an obstacle to reasonable and prudent guidelines.