Next Tuesday, Mississippi voters will decide whether to amend the state constitution by casting ballots on a one-sentence bombshell: "Should the term 'person' be defined to include every human being from the moment of fertilization, cloning, or the equivalent thereof?" The "personhood" measure is being pushed by Colorado-based anti-abortion group Personhood USA. The amendment is expected to pass, and would presumably outlaw all abortion in the state. Here's what you should know:

The amendment would outlaw abortion?
Abortion rights are the most obvious casualty, and that's how proponents of the measure are selling it to Mississippi's socially conservative voters. If a fetus is legally considered a person, abortion would fall under homicide laws. "Will personhood end abortion in Mississippi?" says Jackson-based OB-GYN Dr. Freda Bush. "Yes. Because we believe abortion is the taking of an innocent human life."

Would this affect practices besides abortion?
Yes. It would almost certainly ban in-vitro fertilization, "which often involves discarding unused (fertilized) embryos," says Jon Fasman in The Economist. Popular types of birth control like the IUD, which can prevent a fertilized egg from implanting in a woman's uterus, would also likely be prohibited, perhaps along with the pill. The measure could also prevent doctors from terminating ectopic pregnancies, where the unviable egg implants in the fallopian tubes or outside the uterus, endangering the woman. "Perhaps most worryingly," says Sarika Bansal at The Huffington Post, "personhood may begin to criminally implicate some women for having stillbirths and miscarriages."

Are these fears realistic?
Legally, the measure is so "profoundly ambiguous" that it's impossible to know, say law professors I. Glenn Cohen and Jonathan F. Will in The New York Times. At what point on the "fertilization" continuum does the law kick in? Is the amendment a set of "first principles" that need legislative action to take effect, or is it a self-executing law that will "immediately redefine thousands of references to 'human beings' or 'persons'" in Mississippi's penal code? Adding to the uncertainty, says in-vitro fertility specialist Dr. Randall Hines, is the fact that the law would "leave it to a local prosecutor to decide who he's going to prosecute and which issue he's going to prosecute on." 

Who's for the measure, and who's against it?
Both men vying to replace term-limited Gov. Haley Barbour (R) on Tuesday, Lt. Gov. Phil Bryant (R) and Hattiesburg Mayor Johnny DuPree (D), back the measure, as do the American Family Association and a broad selection of other anti-abortion groups. The American Civil Liberties Union, Planned Parenthood, and some medical organizations oppose it. But many anti-abortion advocates are also opposed, or at least on the fence: Some, like Barbour, worry about the unintended consequences; others, like Mississippi's Catholic bishops and the National Right to Life Committee, are warning that the personhood amendment could harm efforts to overturn Roe v. Wade.

Speaking of which, doesn't this amendment violate federal law?
It almost certainly runs afoul of Roe v. Wade — but that's the point, says The Economist's Fasman. "Advocates wish to provoke a series of court challenges leading all the way up to the Supreme Court, whose current composition is far less favorable to abortion-rights advocates than was the early-1970s Burger Court, which decided Roe." But if the Supreme Court strikes Mississippi's law down, warns the National Right to Life Committee's James Bopp, it "would jeopardize all current laws on abortion." The anti-abortion movement succeeds when it forces its opponents to defend extreme practices, like late-term abortions, Bopp says. Personhood proposals are a harder sell.

Sources: Washington Post (2), New York Times, Economist, NPR, Huffington Post, CBS News, U.S. Catholic