How to shut up people who are against abortion

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I, and I'd guess most people, would count 2 days as negligible. Half a week is 3 days or more. Medical professionals and their literature typically state pregnancy lasts 10 months. It gets knocked down to 9 because the first month it's virtually impossible to detect the pregnancy. Unless the woman is having daily blood tests screening her HgC levels.
ETA: I bring this up because the abortion debate often comes down to key points of fetal development. Which often occur sooner than the pro-choice camp wants to admit, and aren't as significant as the pro-life camp chooses to believe. Speaking in generalities of course