It's unlikely that a fetus can feel pain until the seventh month of pregnancy, according to a review of medical literature by San Francisco researchers.

Their conclusion raises questions about efforts by anti-abortion advocates to push for laws requiring that physicians discuss fetal pain issues with expectant mothers considering abortions after the fifth month.

The review, published in today's Journal of the American Medical Association found that the brain's neurological pathways which allow for the conscious perception of pain do not function until after the 28th week of pregnancy.

"Just having the wiring doesn't tell you that the lights can go on," said Dr. Eleanor A. Drey, one of five researchers at the University of California at San Francisco who wrote the report. "Our review shows that it doesn't happen until well into the third trimester."

Women should not be exposed to the added health risks of fetal anesthesia if there is no evidence that such pain can be felt, the authors said.

Nevertheless, the researchers said anesthesia is warranted during life-saving surgery before the 28th week because the medicine has other advantages, such as inhibiting fetal movement during surgery.

The study comes as fetal-pain legislation is pending in Congress. The Unborn Child Pain Awareness Act, sponsored by Sen. Sam Brownback, R-Kansas, and U.S. Rep. Chris Smith, R-New Jersey, would require that a doctor tell a woman who is considering abortion and is 20 weeks pregnant or more that "there is substantial evidence" the fetus will feel pain. The mother would then have the option to seek anesthesia for the fetus during the procedure.

Abortions at 20 weeks after fertilization would cause "severe and excruciating" pain to the fetuses, according to Dr. Kanwaljeet "Sonny" Anand, a pediatrician at the University of Arkansas for Medical Sciences and an expert on fetal pain. Anand testified last year in federal court in a case about late-term abortions.

Several states have enacted fetal-pain laws and others are considering legislation. Arkansas, which enacted the first law this year, requires physicians to discuss pain issues with their patients. Doctors in Minnesota are grappling with ramifications of an anesthesia requirement that was passed by the state Legislature last month.

Pennsylvania does not have a fetal-pain law, nor has any legislation been introduced, said Mary Beliveau of the Pennsylvania Pro-Life Federation.

The majority of abortions take place during the first three months. Only 1.5 percent of abortions are performed at 20 weeks of pregnancy or later.

Douglas Johnson, legislative director at the National Right to Life Committee in Washington, D.C., yesterday blasted the study and assailed the motives of the researchers, including Drey, an administrator of the university's Center for Reproductive Health Research and Policy, which he described as a "pro-abortion center."

He argued it is commonplace for newborns to survive now at 23 weeks. Anesthesia is given to a premature baby at this stage if doctors do a surgical procedure.

"It defies common sense that a baby has the capacity for pain when born at 23 weeks, but does not have this capacity in utero at 27 weeks," Johnson said.

The authors' aim, he said, was to develop information that would convince abortion practitioners that they do not have to discuss fetal pain with their patients.

"That's the bottom line," he said.

The researchers rejected those views and said the growing number of laws regarding notification of fetal pain has raised significant clinical, ethical and policy issues. They pored over scores of studies and medical reports to try to get a handle on fetal pain.

"It's an issue coming up in legislatures," Drey said. "As academic physicians and researchers, our obligation is to try to help review the evidence. It also is an issue that is relevant for patient care."

Researchers who claim fetal pain can be felt earlier in development note the release of stress hormones and movement of the fetus in response to painful stimuli.

Although the researchers acknowledged that data is limited, they stressed that neither withdrawal reflexes nor hormonal stress responses to invasive procedures prove the existence of fetal pain. These responses also can be elicited other ways.

"You can have release of those same stress hormones during exercise," Drey said.

Pain is an emotional and psychological experience that requires conscious recognition of painful stimuli, the researchers wrote. All such connections in the brain have not been linked until later in fetal development.

Fetal anesthesia or analgesia should not be recommended or routinely offered for abortion because current experimental techniques provide unknown fetal benefit and may increase risks for women, such as hemorrhaging and other complications.