Gov. Jan Brewer and the Arizona Legislature performed a biological miracle Thursday when they decided that pregnancy begins at menstruation — not the moment of conception — in a pack of adjustments to abortion regulations that will ban most of the procedures 20 weeks after the start of a woman’s last period.

Abortions after that time will be legal only when they are deemed necessary to prevent the mother’s death or “substantial and irreversible impairment of a major bodily function.” Ultrasounds will also be required 24 hours before the procedures. –ARK