Saying the ban is merely a regulation is a "fabrication," said Janet Crepps, a Center for Reproductive Rights lawyer helping represent three Arizona OB-GYNS whose lawsuit challenged the ban. "For some women, it's an outright ban prior to viability."
While most of the other 20-week bans start the age calculation from a supposed date of conception, Arizona's version begins with the first day of the woman's last menstrual period. For most women, that would be about two weeks earlier than conception.
However, Arizona's ban includes a yet-to-be-determined amount of wiggle room because the ban also tells doctors to use also other accepted medical practices, such as ultrasound exams, when determining a fetus' age.
Arizona's abortion law already used the last menstrual period as a dating technique before the ban was enacted, and its use isn't controversial by itself because it's a standard starting point in obstetrics for calculating a due date.
"LMP is the gold standard," said Crepps, the Center for Reproductive Rights lawyer.
However, she and other critics of the ban said applying that measurement to a 20-week abortion ban both crosses a legal line and imposes hardships on women who might chose to abort pregnancies in the weeks immediately before viability.
Legislative supporters of the ban relied on testimony by Dr. Allan Sawyer, a Phoenix-area OB-GYN opposed to abortion, that it'd be very rare that fetal anomalies that might prompt women to get abortions couldn't be detected earlier than 20 weeks of pregnancy.
Sawyer said ultrasounds and blood tests can detect abnormalities fairly early in pregnancies, well before 20 weeks.
That means women would have "time to make a decision on whether or not to abort," said Rep. Kimberly Yee, the sponsor of the abortion bill that included the ban.
However, an Arizona OB-GYN opposed to the ban said many women don't have early ultrasounds because of limitations of insurance coverage and that some don't learn of anomalies such as the lack of a brain stem until right at about 18 or 19 weeks. Then it takes time to get a confirming diagnosis from a specialist, said Dr. Maria Manriguez.
"By the time they get an appointment, it could easily be 20 weeks and that person is not able to terminate that pregnancy that could not be viable," said Manriguez.
According to Arizona Department of Health Service statistics, 188, or 1.4 percent, of the 13,606 abortions reported to the state as being performed in 2011 were at gestational ages of 20 or more weeks as measured by a woman's last menstrual period.