IF FETUSES could talk, legislating on their behalf would be a lot easier. But in the absence of direct testimony, politicians are taking significant decisions about fetal welfare based on controversial claims about whether or not they can feel pain.
In the US, for example, a government openly opposed to abortion claims that fetuses feel pain from 20 weeks after conception. Congress is even considering proposing federal laws that would force doctors to inform women seeking an abortion of this, and to offer them the opportunity to have their fetus anaesthetised. Arkansas and Georgia enacted similar state laws this year, and dozens of other states are considering doing the same.
But two new reviews of fetal pain, one from the US and one from New Zealand, suggest the proposed laws might be misguided and based on evidence that is out-of-date and prone to misinterpretation.
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Both reports say there is an emerging consensus that fetuses do not have the brain circuitry to feel pain until 29 weeks into a pregnancy. The New Zealand researchers go further, concluding that the fetus is likely to be unconscious throughout pregnancy, existing in a sleep-like state and unable to sense pain. That means doctors who advocate giving analgesia to fetuses during surgery not aimed at abortion should think again. Although few studies have been done, there is emerging evidence that anaesthetics may actually harm the growing baby, the review says.
鈥淒octors who advocate giving analgesia to fetuses having surgery should think again. They may do more harm than good鈥�
The US research, authored by Mark Rosen of the University of California, San Francisco, and colleagues, says that although the thalamus of a fetus less than 29 weeks old can receive nerve signals that a conscious person would interpret as pain, their sensory cortex lacks the circuitry to receive and interpret the signal (Journal of the American Medical Association, vol 294, p 947). 鈥淭he capacity for perception cannot exist before the circuitry develops, and even then, functional capacity probably requires even more time to develop,鈥� says Rosen.
His paper also rejects the idea that fetuses must feel pain because they flinch away from injections, grimace when exposed to pain during in utero surgery and experience surges of stress hormones during 鈥減ainful鈥� procedures. The authors argue the same events happen in brain-dead adults and anaesthetised adults undergoing surgery, and even in anencephalic babies, which have no sensory cortex.
The key thing, Rosen says, is that pain is a psychological construct based on experience and memory, and so has to be 鈥渓earned鈥� even if the necessary brain circuitry is complete. 鈥淧ain is a complex sensory experience requiring some level of consciousness, and this is substantially different from reflex responses or stress responses.鈥�
Some experts attending the 11th World Congress on Pain in Sydney, Australia, last week disagree. Lars Arendt-Nielsen, a leading pain expert at Aalborg University in Denmark and a reviewer of the JAMA paper, says too much emphasis is placed on the idea that you need a functioning cortex to feel pain. He says patients who have had their sensory cortex removed, or have suffered a brain injury or tumour in the region, still report perceiving pain.
鈥淧ain is a psychological construct based on experience. It needs some level of consciousness and has to be learned鈥�
However, the New Zealand research, published by David Mellor of Massey University in Palmerston North and colleagues in Brain Research Reviews (DOI: 10.1016/j.brainresrev.2005.01.006), says that babies are sedated and unconscious throughout pregnancy, as both the fetal brain and placenta produce potent sleep-inducing hormones, including the neurosteroidal anaesthetic pregnanolone.
That view is backed by Maria Fitzgerald of University College London, a co-author of a report into fetal awareness by the UK Royal College of Obstetricians and Gynaecologists in 1997. 鈥淚t is unlikely that the fetus is ever awake or aware at any point during gestation, due to the high levels of endogenous neuroinhibitors,鈥� she says.
More recently, Mellor and his colleagues have reviewed experiments which challenge the assumption that towards the end of pregnancy, babies spend around 5 per cent of the time fully awake. 鈥淲e鈥檝e explored this at some depth and come to the conclusion that those periods of wakefulness are actually sleep transitions from one state to another,鈥� says Mellor.
His conclusions are also supported by David Walker of Monash University in Melbourne, Australia, who has performed experiments on sheep fetuses. These usually produce very similar physiological results to those seen in humans. Chemically blocking the production of some of the sleep-inducing hormones actually triggers a burst of electrical activity in the brain and muscles of a sheep fetus, says Walker. Other experiments show that the higher areas of a sheep鈥檚 brain receive no sensory information until after birth.
That supports the notion that hormones actively suppress mental activity in the fetus. 鈥淭he purpose is for the baby not to be able to perceive a lot of physical sensation, because otherwise it would be reacting to things it can鈥檛 do anything about.鈥�
That also means doctors are wrong to assume that because a premature baby can feel pain, a fetus of the same age can too. If anything, it would not benefit a fetus to do so, as it cannot alleviate its discomfort or move to escape what is causing the pain.
There is concern that giving fetuses painkillers such as morphine during surgery could actually harm them. Mellor points to work showing that morphine causes vigorous breathing movements in a sheep fetus, which forces its muscles to consume more oxygen than available through the placenta. 鈥淥n the basis of our review, we recommend great caution before giving analgesics and anaesthetics to the fetus if your purpose is fetal well-being,鈥� he says.
