The most egregious provision measures the gestational age of the fetus according to the first day of a woman’s last menstrual period (LMP), instead of the widely accepted post-fertilization age.
Calculating a pregnancy by the last menstrual period is often inaccurate due to the irregularity of menstrual cycles and the uncertainty of the exact point of fertilization. Doctors typically approximate pregnancies from the point of fertilization, which is up to two weeks after LMP. Implantation, or when the fertilized egg implants in the uterine wall, usually occurs a week after fertilization—three weeks from LMP.
So, when the Arizona legislature says no abortions after 20 weeks, they really mean about 18 weeks from fertilization and 17 weeks after implantation.
With this bill, Arizona is essentially redefining where life begins–to before conception. By that logic, whenever a woman has her period or is releasing an ovum into her fallopian tubes, she’s pregnant.
UPDATE: This is from here. And everyone in comments has made it very clear that the criticism above really isn’t a legitimate one. Moral of this story: don’t blog before coffee. It seems like a good idea. So efficient. But really, not a good idea at all.