Up until a few years ago, it was thought that the human fetus undergoing an abortion was oblivious to pain, but scientific advances have revealed new information that entails ethical dilemmas related to interventions with fetuses.

A lecture presented on 15 February, 2022, at the Conference on Retroviruses and Opportunistic Infections CROI 2022 provided evidence on the ability of fetuses to feel pain, obtained after anatomical, physiological and embryological study. The researchers were able to observe signs of crying and other reactions through movements and blinks, which show the ability of the fetus to be excited by external stimuli, such as loud or sudden noises. It has also been seen that, in intrauterine surgeries, vital parameters such as heart rate, respiratory changes or stress hormones vary in response to an invasive procedure. All of this poses a dilemma about limits in fetal surgery, in which there is a need to evaluate when the development of pain perception begins and when it becomes conscious, among other things, to adequately weigh the harm that may be inflicted on the fetus in these procedures. Accordingly, they can be adapted in a way that respects the dignity of the fetus, as occurs in any other intervention.

In 1989, Anand and Carr published a large study describing fetal development in relation to pain perception, explaining how, during the first trimester of pregnancy, the amygdala — the brain’s fear and anxiety center — develops from the diencephalon and telencephalon (1). At the same time, synapses occur between the sensory fibers and the receptor neurons in the dorsal horn of the spinal cord (2). Furthermore, the receptors responsible for the neural process of signaling tissue damage, the nociceptors, are distributed in the skin of the fetus in the same proportion as in the adult, first in the skin (weeks 11 and 15) and later in the mucous membranes (week 20), in addition to the production of neurotransmitters (3).

In the second trimester, between weeks 14-26, the subplate, a primordial structure in the fetal brain for processing thalamocortical information develops and, later, the thalamocortical connections (4).

By the end of the second and beginning of the third trimester, the nociceptive pathways are considered complete. From week 29-30, we can consider that the capacity for conscious awareness is present (5); the only difference is incomplete myelination of the nerve pathways at week 37. The myelin sheath allows impulses to be transmitted quickly and efficiently along the neurons, so their absence does not make transmission impossible, but simply slower.

According to the International Association for the Study of Pain (IASP), pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage”. Moreover, this is always subjective and subject to the experience. However, as stated in a recent article published in the journal Cuadernos de Bioética, “Several authors have expressed their dissatisfaction in relation to the rejection of fetal pain based on a definition that does not include people who are not aware of their own body or who cannot describe it, as is the case of people with cognitive disabilities, newborns and presumably fetuses”.

Consequently, this definition that excludes so many people should be expanded.

This redefinition of the ability to perceive painful stimuli affects numerous procedures, such as prenatal diagnosis, fetal surgery and, above all, abortion. The recognition, based on this evidence, that the fetus on which the abortion is performed is capable of experiencing pain, could change the attitude of some women and healthcare professionals involved, who might reconsider their decision to participate in abortions.

With regard to fetal surgery or prenatal diagnosis, the need to administer anesthesia should be evaluated to try to alleviate the suffering to which the fetus may be subjected, as to do otherwise would be acting on the fetus in a maleficent way.

The diversity of opinions about when human life begins in the womb, as well as when the embryo or fetus should be considered a person, makes it difficult to afford them fair treatment, like any other patient, with dignity and rights.

It is the duty of physicians and healthcare workers, as well as of society as a whole, to address this issue, to comply with what is stated in the Declaration of Geneva in the sense that “there is an urgent need for direct and effective action to tackle the root causes of threats and violence against us”.


Paloma Aznar and Julio Tudela

Bioethics Observatory – Institute of Life Sciences

Catholic University of Valencia


1 Muller, F., O´Rahilly, R. “The amygdaloid complex and the medial and lateral ventricular eminences in staged human embryos”. J Anat. 2006; 208 (5): 547–564.

2 Anand, K. J. S., Hickey, P. R. “Pain and its effects in the human neonate and fetus”. New England Journal of Medicine. 1987; 317: 1321-29.

3 Tadros, M. A., Lim, R., Hughes, D. I., Brichta, A. M., Callister, R. J. “Electrical maturation of spinal neurons in the human fetus: comparison of ventral and dorsal horn”. J Neurophysiol. 2015; 114 (5): 2661-71.

4 Kostović, I., Judas, M. “The development of the subplate and thalamocortical connections in the human fetal brain”. Acta Paediatr. 2010; 99: 1119-27.

5 Lee, S. J., Ralston, H. J., Drey, E. A., Partridge, J. C., Rosen, M. A. “Fetal pain: a systematic multidisciplinary review of the evidence”. JAMA. 2005; 294: 947-54.



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