With Roe v. Wade, the U.S. Supreme Court gave states the right to legislate abortion restrictions during a woman's second trimester. Many states enacted laws that make it more difficult to terminate a pregnancy. Among them, Arkansas, Minnesota, and Georgia require physicians to tell women that 20-week-old fetuses can feel pain during the procedure unless they are anesthetized. A newly released review of the scientific evidence, however, suggests the premise of those laws is wrong.
Fetuses cannot feel pain until at least the 28th week of gestation because they haven't formed the necessary nerve pathways, says Mark Rosen, an obstetrical anesthesiologist at the University of California at San Francisco. He and his colleagues determined that until the third trimester, "the wiring at the point where you feel pain, such as the skin, doesn't reach the emotional part where you feel pain, in the brain." Although fetuses start forming pain receptors eight weeks into development, the thalamus, the part of the brain that routes information to other areas, doesn't form for 20 more weeks. Without the thalamus, Rosen says, no information can reach the cortex for processing.
Fetuses do have reflex reactions that can make them seem pained, Rosen says. "If you see a fetus in utero react to needle stimulation, then the common conclusion is that it must feel." But just as with paraplegics, "that's a reflex that's mediated by the spinal cord; that's not a conscious reaction," he says. It is possible that a temporary structure of neurons that appears in a fetus's brain during the second trimester allows it to sense pain. But Rosen and his colleagues believe a fetus's brain doesn't function coherently enough to be conscious.
The use of fetal anesthesia is justified during other surgeries, Rosen says, to block the production of stress hormones. In the case of abortion, he says, it is not necessary and puts the mother at increased risk of adverse reactions, and even death.