Fetuses First Perceive Pain at 35 to 37 Weeks, Study Suggests

September 13, 2011 — Premature infants begin to discern pain from touch at about 35 to 37 weeks of gestation, about two to four weeks before typical delivery, according to a new study in the journal Current Biology, ABC News reports. The findings could shed light on a point of contention in the abortion-rights debate and potentially affect clinical care for preterm infants.

Researchers used electroencephalography to compare preterm infants' brain activity in response to a touch and a heel prick. Infants born at 28 to 35 weeks of development showed comparable brain activity for the touch and heel prick, but infants born at more than 35 weeks of gestation exhibited a greater response to the heel prick than the touch.

Six states have enacted laws banning abortion after 20 weeks of pregnancy, the point at which many antiabortion-rights advocates claim that fetuses can feel pain. "The findings ... should help inform the pain perception portion of the abortion debate," Sessions Cole of the Washington University School of Medicine in St. Louis said. Cole added, "Although this study specifically addresses brain wave differences between premature and term infants, not fetuses, after (receiving) painful and tactile stimuli, it suggests that brain maturation required for fetal pain perception occurs in late pregnancy, more than 11 weeks after the legal limit for abortion in the United States."

The findings also might explain why infants born prematurely have an abnormal pain response, the researchers said. "Clinical practice changed about two decades or more ago to take into account the pain response of premature infants and term infants," lead author Eliot Krane, professor of anesthesia and pediatrics at Stanford University School of Medicine, said in a statement. Krane added, "Clinical practice continues to evolve as we become more cognizant of the deleterious effect of pain in infants" (Conley, ABC News, 9/8).