THE SENSITIVITY TO PAIN OF LATE-SECOND-TRIMESTER BABIES.(Brief Article)

Editor's note. The following excerpt is from an article written by Dr. Paul Ranalli that appeared in the November 1997 issue of NRL News.

As revealed by other work, the late-second-trimester fetus, like the similar-aged premature newborn, likely develops the capacity to be more sensitive to pain than a full-term baby, or even an adult. This is because the inhibitory, pain-modifying network lags in embryologic development behind the establishment of the pain system.

Neurons from the higher reaches of the brain send fibers down to synapse with the thalamus (a key pain-relay station deep in the brain) and the spinal cord, where incoming pain signals from the trunk and limbs are directed upward to the brain. These neurons secrete brain chemicals (serotonin, norepinephrine, and dopamine) which inhibit pain in adults.

Yet, while the pain system is up and running by 20-24 weeks' gestation, this pain-modifying system does not begin to make its appearance until later in pregnancy, continuing to develop until full term and beyond. Thus there is a key period of mismatch, from 20 weeks onward: raw pain impulses from the body may roar through unchecked by the modifying inhibitory mechanism that helps to blunt pain in adults, leaving the unborn child at this stage vulnerable to a degree of pain that is ...