FILE PHOTO: Abortion-rights campaigners attend a rally against new restrictions on abortion passed by legislatures in eight states including Alabama and Georgia, in New York City, U.S., May 21, 2019. REUTERS/Jeenah Moon

(Reuters) - A federal judge on Friday blocked a Mississippi law that would ban abortions once an embryonic heartbeat is detected, which can occur at six weeks after conception, often before a woman even realizes she is pregnant.

Mississippi Governor Phil Bryant, a Republican, signed the so-called “hearbeat bill” into law in March, and the measure had been due to take effect on July 1.

Mississippi is one of several states, including Georgia and Alabama, where Republican-controlled legislatures have enacted strict anti-abortion measures this year in direct challenge to the U.S. Supreme Court’s landmark 1973 Roe v. Wade decision legalizing a woman’s right to terminate her pregnancy.

Roe held that the due process clause of the 14th Amendment provides a fundamental right to privacy protecting a woman’s right to abortion, though it allows states to restrict the procedure from the time a fetus can viably survive outside the womb, which the opinion placed at 24 to 28 weeks from conception.

The measure blocked on Friday was the second legislative bid in less than a year to restrict abortions in Mississippi, a state where only a single abortion clinic remains in operation.

Last November, U.S. District Judge Carlton Reeves struck down an earlier Mississippi law that would have banned most abortions after 15 weeks of pregnancy, ruling it “unequivocally” violates women’s constitutional rights.

“Here we go again, Mississippi has passed another law banning abortions prior to viability,” Reeves said in his latest ruling to block the “heartbeat” abortion ban.

The measure would prevent a woman’s free choice, “which is central to personal dignity and autonomy,” the judge wrote in granting the preliminary injunction. The measure was challenged in court on behalf of the Jackson Women’s Health Organization, the state’s lone abortion facility.