A review of about 1,500 scientific studies concludes that it is highly unlikely that fetuses can feel pain before the 29th week of pregnancy -- a finding that contradicts several pieces of proposed abortion legislation.
The review, published today in the Journal of the American Medical Assn., comes as Congress and state legislatures are considering bills that would require physicians to tell pregnant women considering abortions that fetuses feel pain and to offer the women anesthesia for the fetuses.
Georgia and Arkansas have implemented such laws and several other states, including California, have considered them.
The federal bill, introduced by Sen. Sam Brownback (R-Kan.) with 33 co-sponsors, includes a script that physicians would have to read to women seeking an abortion in the fifth month or later. It says: "The Congress of the United States has determined that at this stage of development, an unborn child has the physical structures necessary to experience pain."
A similar bill has been introduced in the House.
The study concludes that, "based on the available evidence, the fetus does not have the functional capacity to experience pain," said Dr. Eleanor A. Drey of UC San Francisco, one of the study's authors.
"That relies on consciousness, and the cortex of those infants is not well enough developed to allow for conscious processing of stimuli" like pain.
Drey said using anesthesia on a fetus when performing an abortion puts the mother's health -- and life -- at risk by slowing her breathing and producing other undesirable effects.
Drey, who performs abortions at UC San Francisco, said the review was conducted to rebut what the researchers perceived to be the inaccuracies of the legislative efforts.
The report echoes the findings of a British panel released eight years ago and will probably not surprise most physicians.
For the last two years, a panel commissioned by the Physicians Committee for Reproductive Choice and Health has been researching the issue "and they reached the exact same conclusions," said Dr. Wendy Chavkin of Columbia University, chairman of the group's board.
Chavkin said she thought the study would probably have little effect on the political debate.
"These laws have nothing to do with pain or pain reduction," Chavkin said. "They are clearly intended to stigmatize abortion, the women who have abortions, and the doctors who provide them."
Critics of the study, including Brian Johnston, head of the western regional chapter of the National Right to Life Committee, said that the review was biased because it was conducted by abortion providers.
Johnston said the physiological responses of premature infants indicated reactions to stimuli.
About 18,000 American women have abortions in the fifth month of pregnancy or later each year.
Dr. Thomas Murphy Goodwin, chief of maternal-fetal medicine at USC, agreed with Johnston.
Premature infants, he said, "appear to be having all the physiological reactions of someone that feels pain later in life."
Their heart rate increases, they release adrenal steroid hormones and they show other effects, he said.
"It's true that it can't be exactly like the pain we [adults] feel, and maybe it is inappropriate to call it pain ... but my gut instinct is that it must be something like pain," Goodwin said.
The problem, both sides agree, is that there is no objective way to measure pain. There is no specific brain wave pattern that indicates pain and no specific chemical marker.
"We have to look at a number of lines of data to decide when the earliest time might be" that pain is perceived, Drey said.
Studies in the medical literature, her team found, indicate that the responses mentioned by Goodwin, as well as the movement of a fetus away from a probing stimulus, are physiological responses like the jerking of a leg when a physician taps the knee with a rubber mallet.