"Back in Washington, Blackmun’s law clerk had substantially revised the draft abortion opinion. He forecast this in an August 4 memo before he finished his clerkship. And then he explained the changes to Blackmun in a memo of August 11, 1972: I have written in, essentially, a limitation of the right depending on the time during pregnancy when the abortion is proposed to be performed. I have chosen the point of viability for this “turning point” (when state interests become compelling) for several reasons: (a) it seems to be the line of most significance to the medical professional, for various purposes; (b) it has considerable analytic basis in terms of the state interest as I have articulated it. The alternative, quickening, no longer seems to have much analytic or medical significance, only historical significance; (c) a number of state laws which have a “time-cut off” after which abortion must be more strongly justified by life or health interests use 24 weeks, which is about the “earliest time of viability.”"