Fetal pain: what does the science say?

Recent years have seen increased attention on the unborn fetus – in particular the question of the fetus feeling pain. Much evidence on this question has come from caring for premature babies in a neonatal intensive care unit (NICU). The modern NICU has allowed babies born as early as 22 weeks (55% of pregnancy) to survive. At 23 weeks, one US hospital reports a 71% chance of survival.

Gestational age at which premature babies had a 50% chance of survival, taken from a range of published studies, together with (for 2015) the hospital mentioned above. The data fits an exponential decay, dropping to 22 weeks by 2040 (although this may not actually be achievable).

Medical staff are generally convinced that premature babies in the NICU can feel pain, and the same is presumably true for unborn babies of the same age. Further attention on unborn babies has resulted from increasingly ubiquitous fetal ultrasounds, from numerous television documentaries on premature babies, and from books, web sites, and apps that encourage pregnant women to track their baby’s development. These have all contributed to the current interest in fetal pain. A 2005 JAMA review on fetal pain was unfortunately tarnished by allegations of conflicts of interest. However, there is a considerable body of other scientific literature on the topic of fetal pain. So what does the literature say?

A premature baby being cared for aboard the US Navy hospital ship Comfort

The question of fetal pain is unfortunately confused by uncertainties regarding the role of the cortex in feeling pain, uncertainties about how the fetal nervous system functions, uncertainties about whether “feeling pain” requires knowing the exact location of the pain, and uncertainties about whether “consciousness” is required to truly feel pain. Furthermore, there are actually two separate human pain systems, one primarily affective (concerning the “hurt” of pain), and the other more discriminative (concerning the location of pain).

A newborn baby, a puppy, and a lobster. Which of these is “conscious”? Which of these can feel pain? Is it acceptable to kill any of these by boiling them alive? Where on this spectrum do human fetuses lie?

However, developmental evidence suggests that the ability to feel pain might begin surprisingly early. Neural pathways to the spinal cord form at 8 weeks. The cerebral cortex begins to form at 10 weeks, although initially it is not connected to the rest of the brain (the cortex continues to develop during pregnancy and long after birth). By 25 weeks, pain-related nerve signals are certainly reaching the cortex. Electroencephalograms have been recorded from 21 weeks. Hearing appears to begin at 18 weeks. At about the same age hormonal stress responses are observed during surgery in the womb. In adults and older infants, such responses are associated with pain. Premature babies show strong responses to pain, and failure to administer analgesia to babies in the NICU undergoing surgical procedures is considered unethical. Surgeons are beginning to administer anaesthesia and analgesia to unborn babies at similar developmental stages as well.

A fetus at 14 weeks

It is widely accepted that the fetus can feel pain from at least 26 weeks, but the threshold at which interventions cause distress may be as early as 20, or even 15, weeks. Obviously, it is extremely difficult to be certain where the threshold lies, since fetuses cannot verbally describe their pain. Yet the same is true for newborn infants and animals, and it has long been accepted that pain in infants and animals is nonetheless real. One surgeon recommends fetal analgesia and sedation for invasive procedures from 23 weeks (coincidentally, the current viability threshold), and a number of other surgeons agree, although some set the threshold several weeks earlier or later. One of the more rational responses I’ve seen says “Scientific data, not religious or political conviction, should guide the desperately needed research in this field. In the meantime, it seems prudent to avoid pain during gestation.” After all, even the possibility of causing unnecessary pain requires preventative action. This would apply both to surgical procedures and, a fortiori, to second- and third-trimester abortion procedures which involve crushing and/or tearing the limbs from a living fetus.

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