Fetal Pain

Recently, JAMA published a survey article on Fetal Pain (the abstract is here, the full text requires a fee). The authors reviewed a large number of research papers relevant to the stage of development at which a human fetus feels pain, and, secondarily, on techniques available for direct fetal anesthesia or analgesia in the case of abortion (or therapeutic interventions). Despite the evidence of reflex responses and hormonal responses by the first and second trimester respectively, the authors conclude that analysis of nervous system development indicates fetal perception of pain is unlikely before the third trimester (29 or 30 weeks gestational age). They note that withdrawal reflexes only require peripheral sensory nerves which connect to motor neurons through the spinal column. They assert psychological awareness of pain requires relatively full cortical functioning, which they conclude comes at about 29-30 months.

The article includes a paragraph acknowledging the context: proposed federal legislation which would require physicians to inform women seeking abortions at 20 or more weeks that the fetus feels pain and to offer anesthesia for the fetus (evidently statutes like this have been enacted in Georgia and Arkansas).

Given the highly charged politics of abortion, the article caught a good deal of attention in the press, and a number of critics have disputed the conclusions and/or complained about pro-choice bias given some of the authors’ past affiliations (links here and here: William Saletan’s take on Slate here). I argue below that a different conclusion from the authors' can be reached from the same set of facts.

My interest in this was similar to my angle in my Terri Schiavo and animal consciousness posts: we have a tendency to think of conscious experience as an all or nothing thing, and I’m interested in exploring the evidence that there is more of a continuum of first person experience from minimal to full tilt.

Echoing what I’ve read elsewhere, the authors say the seat of awareness is in the thalamocortical circuitry. While they found no studies of such circuits in fetuses as they relate to pain specifically, they (reasonably) infer conclusions from looking at work on other pathways (like visual and auditory). Now, curiously, the specifics of these studies don’t seem to precisely support the survey article’s conclusion, since they show thalamic projections reaching the cortex at 23-27 weeks. A later part of the paper on electrical activity is invoked to buttress the 29-30 week figure in the conclusion, but this seemed to my amateur eyes less compelling (more indirect) evidence on the question.

Importantly, the authors include a paragraph noting that others have proposed that connection to the cortex could be established indirectly if afferents from the thalamus reach a transient cortical subplate which appears earlier while the layers of the mature cortex are still forming. This happens by 20 to 22 weeks. Given the lack of firm evidence that this connection conveys pain information (as we understand it in fully developed context) the authors don’t give it weight in their conclusion.

The authors do not address the broader question of whether something similar to pain (if more primitive in some sense) exists during development absent any pathway to even a primitive cortical subplate. Is there something in-between the reflex arc and the cortical arc which gives rise to pain-like sensation? At this point we probably have no evidence and can only speculate. But I think it is a reasonable intuition that in different stages of development, intermediate stages of experience may exist.

My problem with this article is not with the factual content, but with the way this is parsed to reach a conclusion. In the absence of compelling evidence that fully developed pain awareness exists prior to 29-30 weeks, the authors conclude it doesn’t. I might place the emphasis differently: while we lack definite confirmation, something similar to our pain awareness might exist at 20-22 weeks, and we just don’t know if a neural response worthy of being compared to pain might exist earlier than that.

I continue to support the legality of abortion; however, I also continue to believe relatively more emphasis should be placed on the procedure being done as early as possible.