Most mothers believe the baby is immune to pain while in-utero, but new research reveals the fetus can feel the difference between pain and normal touch as early as 35 weeks gestation. Starting at 35 weeks, the brain changes rapidly; evolving from immature to adult-like in just a few weeks. Before 35 weeks gestation, the brain reacting similarly to normal touch and pain, but after the fast maturation of the brain between weeks 35 and 37, the brain reacts differently to normal touch and pain.

Researchers followed 46 infants, some born full-term and others between 28 and 37 weeks gestation. All tests were completed after the infant was born. Testing took place using an EEG, electroencephalography, during a heel prick. Heel pricks are used to draw blood for normal infant testing. The EEG measured brainwaves at the time of the prick to determine how the brain reacted to pain.

Infants born prematurely reacted to painful stimuli with a general brain response, not unlike the response to normal touch. At about 35 weeks gestation, the brain response changes to a more focused reaction, which means the infant's brain understands the difference between two different types of touch, specifically normal touch and painful touch.

Previous research on brain development between weeks 35 and 37 of gestation noted a significant change in visual perception during this time. Researchers believe the golden period for brain development is weeks 35, 36 and 37, which supports the need to prolong pregnancies as long as possible for optimal brain development.

While researchers know brain reactions are different prior to the 35th week and after the 35th week, there is no indication that a premature infant does not feel pain. Brain activity and the neural response is different than the physical reaction to pain. It is highly likely that premature infants feel pain, but the brain does not uniquely respond to painful stimuli until after the 35th week of gestation.

Source: Lorenzo Fabrizi, Rebeccah Slater, Alan Worley, Judith Meek, Stewart Boyd, Sofia Olhede, Maria Fitzgerald. Current Biology. 8 September, 2011.