An Evidence-Based Discussion of Fetal Pain and Stress

Background: The concept of fetal pain results from procedures conducted without anesthesia in preterm newborns and fetuses, which indicate that it is possible to examine fetal pain based on stress hormone, metabolic, and behavioral changes. Anatomical and physiological data suggest that fetuses become capable of processing nociceptive stimuli around midgestation, although the associated changes in fetal brain development remain unclear. What constitutes fetal pain remains controversial in the light of the definition of pain adopted by the International Association for the Study of Pain (IASP), which posits pain as an “unpleasant sensory and emotional experience.” Summary: Here, we examine the notion that human fetuses cannot “experience” pain and potential implications of this claim. We highlight the key scientific evidence related to fetal pain, including clinical studies on pain in fetuses and preterm newborns. We argue that consistent patterns of stress hormones, metabolic changes, body movements, hemodynamic changes, and pain-related facial expressions in fetuses exposed to invasive procedures overcome the need for subjective proof of pain as articulated in the IASP definition. No study to date has conclusively proven the absence of fetal pain beyond the age of viability. Key Messages: Based on the current evidence, we propose that all fetuses receive anesthesia regardless of the invasive procedures being performed to guarantee the least possible pain and physiological, behavioral, or hormonal responses without exposing the mother or her baby to unnecessary complications.

The presence and timing of pain perception during fetal development (i.e., before birth) have remained controversial for many decades. Until recently, surgeons had to wait for the baby’s birth to surgically correct any congenital malformations, but now such surgeries are conducted while the baby is still in the mother’s womb. Other invasive procedures are also performed, like blood transfusions, before the baby’s birth. These invasive procedures cause dramatic changes in the stress hormones, metabolism, and behaviors of the fetus – similar to those of premature newborns undergoing such procedures. Changes in the brain and other physiological systems also suggest that fetuses become capable of processing noxious stimuli about halfway through pregnancy, although their reactions may not meet the international definition of pain. In this article, we describe the key scientific evidence related to fetal pain, including clinical studies on fetuses and premature babies. We propose that sufficient data are available to serve as proof of fetal pain in the latter half of pregnancy and that no study to date has conclusively proven the absence of fetal pain beyond the age of viability. Based on this evidence, we propose that all fetuses receive anesthesia regardless of the invasive procedures being performed to guarantee the least possible pain and physiological, behavioral, or hormonal responses without exposing the mother or her baby to unnecessary complications.