Arizona's severe new abortion law is set to go into effect this week, thanks to a federal judge who ruled it constitutional. The law, signed by Republican Gov. Jan Brewer earlier this year, forbids doctors from aborting fetuses with a gestational age of 20 weeks or older, which is before the 23- to 24-week milestone when a doctor can confirm that a pregnancy will likely not result in a miscarriage, a stillborn, or an infant who will die soon after being born. That means some women could have to give birth to stillborn babies. The law has been assailed by abortion-rights advocates and civil-rights groups, who say it violates Supreme Court precedent and will cause wanton emotional damage to mothers. Here, a guide to what has been described as the "most extreme" abortion ban in America:

What does the law say exactly?
In addition to banning abortions after 20 weeks, the law defines the period of gestation as beginning when the mother has her last period. Since very few women get pregnant immediately after their last period — generally, conception comes a couple weeks later — the ban effectively applies to what would otherwise be labled as 18-week pregnancies. 

Why did the judge rule that the law was constitutional?
Judge James Teilborg of the U.S. District Court in Arizona said the ban was legal because it provided an exception when a mother's life is in danger, which he argued meant that it was not a total ban. Teilborg also said Arizona's lawmakers were justified in passing the law "by evidence that a fetus can feel pain as soon as 20 weeks after conception," says Warren Richey at The Christian Science Monitor. However, critics say Teilborg completely ignored a Supreme Court precedent that bars pre-viability abortion bans. 

Will abortion-rights groups appeal? 
Yes. Critics of the law hope it will be struck down by a federal appeals court. In the meantime, the American Civil Liberties Union is requesting "an emergency state of the law, to bar it from coming into effect" on August 1, says Sarah Kliff at The Washington Post.

How will the law affect pregnant women?
The greatest fear is that "mothers of babies with fatal birth defects will be forced to carry their pregnancies to term, give birth, and then watch their babies die," says Erin Gloria Ryan at Jezebel. For example, the law forbids a mother from aborting a baby diagnosed in the womb with anencephaly, "a neural-tube defect in which babies develop without most of their brain or skull," says Alia Beard Rau at The Arizona Republic. In addition, mothers will likely be forced to give birth to stillborns. 

How many women will this impact?
Not many. Only about 100 women in Arizona have abortions after the 20-week period per year, and "it's unclear how many of those are because of a problem with the pregnancy," says Rau. However, that same state shows that "if lawmakers want to reduce the number of abortions occurring annually in the U.S., banning late-term procedures isn't the way to do it," says Ryan.

Sources: The Arizona Republic, The Christian Science MonitorJezebelThe Washington Post