ATLANTA — A federal judge on Tuesday temporarily blocked Georgia’s restrictive new abortion law from taking effect, following the lead of other judges who have blocked similar measures in other states.

The law signed in May by Republican Gov. Brian Kemp bans abortions once a “detectable human heartbeat” is present, with some limited exceptions. Cardiac activity can be detected by ultrasound as early as six weeks into a pregnancy, before many women realize they’re expecting, according to a legal challenge.

The law had been scheduled to become enforceable on Jan. 1.

Lawyers with the American Civil Liberties Union, Planned Parenthood and the Center for Reproductive Rights in June filed a constitutional challenge to the law on behalf of Georgia abortion providers and an advocacy group.

US District Judge Steve Jones wrote in an order Tuesday that the current laws governing abortion in the state shall remain in effect for the time being. Based on current US Supreme Court precedent, he wrote, the challenge to the new law is likely to succeed.

Kemp spokeswoman Candice Broce said in an email that the governor’s office is reviewing the decision.

“Despite today’s outcome, we remain confident in our position,” she wrote. “We will continue to fight for the unborn and work to ensure that all Georgians have the opportunity to live, grow and prosper.”

“Today is a tremendous victory for the women of Georgia and for the Constitution,” ACLU of Georgia legal director Sean Young said. “Politicians have no business telling women or couples when to start or expand a family. This case has always been about one thing: Letting her decide.”

The law defines a “detectable human heartbeat” as “embryonic or fetal cardiac activity or the steady and repetitive rhythmic contraction of the heart within the gestational sac.” Referring to a document from the American College of Obstetricians and Gynecologists, the legal challenge says that “cells that eventually form the basis for development of the heart later in pregnancy” produce “cardiac activity” that can be detected by ultrasound as early as six weeks into a pregnancy.

The law makes exceptions in the case of rape and incest, as long as the woman files a police report first. It also allows for abortions after cardiac activity is detected when the life of the woman is at risk or when a fetus is determined not to be viable because of a serious medical condition.

Additionally, it declares an embryo or fetus a “natural person” once cardiac activity can be detected, saying that is the point where “the full value of a child begins.” That would make the fetus a dependent minor for tax purposes and trigger child support obligations.

The Supreme Court has “repeatedly and unequivocally” held that a state cannot ban abortion prior to viability and Georgia’s law does precisely that because fetal cardiac activity can be detected months before the point of viability, Jones wrote. He noted that other courts have “uniformly and repeatedly” struck down other attempts to ban abortions prior to viability.

The judge also was concerned by the part of the law that redefines “natural person” to include “any human being including an unborn child,” which is defined as an embryo or fetus “at any stage of development who is carried in the womb.”

In its landmark Roe v. Wade ruling in 1973, which legalized abortion nationwide, the Supreme Court considered and rejected that precise definition, Jones wrote.

The challenge to the law argues that it is unconstitutionally vague. Certain medical treatment can negatively affect a pregnancy and it’s unclear whether providers could be criminally prosecuted since the new law confers personhood on a fetus, the complaint says.

It is likely that the challenge will succeed in its argument that the law is too vague for ordinary people to understand what’s prohibited, Jones wrote. It is also likely correct that the new personhood definition could leave medical providers who treat pregnant women “open to arbitrary or discriminatory enforcement,” he wrote.

Georgia’s current abortion laws prohibit abortions at 20 weeks or more “from the time of fertilization,” unless the fetus has a defect so severe that it is unlikely to live or if a doctor reasonably finds that an abortion is necessary to protect the life or health of the mother.

The so-called heartbeat law is one of a wave of laws passed recently by Republican-controlled legislatures in an attack on Roe.

None of the bans has taken effect. Some have already been blocked and elsewhere courts are considering requests to put them on hold while legal challenges play out.