Fetal pain: implications for research and practice

Abstract

Pain is a subjective experience. The fetus cannot tell us what it is feeling, and there is no objective method for the direct measurement of pain. To address the question of pain in the fetus, one must use indirect evidence from a variety of sources, and then make an informed guess. This approach is similar to that which we use with animals. We cannot ask animals how they feel, but infer from a variety of indirect approaches including study of their behaviour, anatomy, and physiology. Does the fetus feel pain? ConsciousnessTo feel pain, or suffer discomfort, one needs to be conscious, to be aware. We do not know when, if at all, consciousness starts in the fetus. The biological basis of consciousness is little understood although at least in adult humans, the evidence suggests that it is in some way associated with electrical activity in the cerebral cortex. Crick' has suggested that one is conscious of something when there is electrical activity in specific large neural cortical networks, particularly in layers IV to VI of the cerebral cortex2.Greenfield has emphasised that one should not think of consciousness as an all or none phenomenon, rather that it may come on like a dimmer switch. This concept of evolving consciousness could apply to the developing fetus, in whom experience is most unlikely to be the same as that of an adult. Furthermore, the fetus may not have the same physical basis for conscious experience as the older human. Frogs, for example, do not have a developed cerebral cortex, lacking layers IV to VI. If they are conscious at all, their experience must be associated with activity in a less complex neuronal network, possibly more analogous to the fetal subplate zone3. Anatomical evidenceThe most important evidence is anatomical. For the fetus to feel pain, it is necessary for the requisite nociceptive pathways to be developed. This involves neural connections between peripheral receptors and the spinal cord, upward transmission via the spinal cord to the thalamus, and from there to the outer cerebral layers. The development of the human nervous system is a progressive and ascending process, with the cerebral cortex the last region to develop.Connections from the periphery to the spinal cord are formed early, at about eight weeks; C fibres begin to grow into the human fetal spinal cord at about 10 weeks4. The substantia gelatinosa in the dorsal horn is the spinal cord region of interneurones which is thought to play a major part in the modulation of noxious inputs; by 30 weeks of gestation it has most features of the adult4. The cerebral cortex starts to form at 10 weeks, although at that stage it is isolated from the rest of the brain5. Cortical development involves the structural differentiation and maturation of cortical neurones, fibres, glia and blood vessels, and this starts only at about 17 weeks of gestation with layers VI and V, but continues until long after birth. From 15 weeks, the cortex is underlain by the subplate zone, a layer of neurones below the cortex that is specific to th...

Fetal Pain: Do We Know Enough to Do the Right Thing?

“…These and other observations support the suggestion that the capabilities of the fetal mind include an experience of pain from at least 26 weeks gestation. 7,9,25 Inferring fetal pain based on these indirect sources of evidence, however, presents notable difficulties. The first difficulty is to account for the many features of the fetal brain that are not similar to that of the adult and older child.…”

“…The thalamic projections that develop from 12-16 weeks are into the subplate. Spinothalamic projections into the subplate have been described as providing a minimal necessary anatomy for pain experience, 9 but this view has to account for the transient nature of the subplate and its apparent role in the maturation of functional cortical connections. The subplate is generally regarded as a ''waiting compartment'' where neurons wait before migrating and forming mature cortical connections in the cortical plate above.…”

“…It is here that my critique diverges from some of the current discussion about fetal pain and sentience. [7][8][9] In my view, it is a mistake to infer subjective experience, including pain, from measures of anatomy, stress hormones and fetal movements, because this approach fails to account for the contents of experience in general, and of pain in particular.…”

Effects on the fetus and newborn of maternal analgesia and anesthesia: a review

“…43,44 Implications for the fetus Neural pathways and neurochemical systems involved in pain perception are functional from mid-gestation, and are well developed by the third trimester. 45,46 Gitau et al conducted a parallel study of the fetal and maternal hormonal response to fetal blood transfusion. They confirmed that the fetus mounts a hypothalamic-pituitary-adrenal response to transfusion via the intrahepatic vein, which involves piercing the fetal trunk, but not to transfusion in the umbilical vein at the placental cord insertion, which has no sensory innervation.…”

“…Hormonal and circulatory stress responses to invasive procedures are observed by 20 weeks. [45][46][47][48][49] Further definition of the neuroanatomical and neurophysiological maturation of sensory pathways involved in pain transmission in the human fetus may provide more direct information about the fetal pain experience.…”