FETAL PAIN. NEW ADVANCES
3. Evidence of fetal pain
4. Some objections
5. The fetus as a patient: analgesia
7. Table 1
Fetuses can feel pain since when their nociceptive system has achieved an adequate development. Recent advances in fetal physiology and imaging show that the fetus’ nervous system is ready from the half of the pregnancy (about 20-22 weeks from conception) to feel pain and to respond to it. This has important clinical and legal consequences.
Can a fetus feel pain? When it was impossible to observe the fetus, or to perform thorough analyses of his/her reactions, this question could have no answer. But in the last few years, some observations have permitted to add details and information on this topic. Four-D-Ultrasound images have given useful data, and physiology advances have shown that the connections of peripheral receptors with the fetal cortex are more precocious than previously supposed, but also that the spino-thalamic connection (a connection with a precocious and deep brain centre) is sufficient to experience pain.
This has a special clinical impact. First, because fetal surgery has moved its first steps (1-5), and now it is evident that in the case of fetal pain analgesia should be provided; second, because fetal pain gives a further evidence of the moral gravity of voluntary abortion, though the absence of pain would not make it less inacceptable.
Here I will highlight some of the main points of this discussion.
3. Evidence of fetal pain.
A Anatomy and physiology The human brain can receive pain stimuli from the half of pregnancy. To this aim, some structures are needed: pain receptors, nerves that transport the stimulus to the thalamus (with the possibility that they have an insulating layer called myelin), neurotransmitters that permit that the stimulus passes from a neuron to another, and a central integration. The central integration is provided by the brain cortex, whose transitory first step is represented by the subplate; but also the thalamus can integrate pain. Table 1 shows the timetable of appearance of the different structures necessary to the sentience of pain (6-11).
B Neurophysiology Is fetal brain active? Fetal magnetoencephalography has been used to effectively record fetal auditory and visual evoked responses and spontaneous brain activity of cortical origin from 27 weeks (12) and at 26-28 weeks GA, evoked potentials may be recorded from somatosensory, visual, auditory and frontal cortices (13). Near infrared spectroscopy with preterm infants, has demonstrated localized somatosensory cortical responses in premature newborn infants from 24 weeks, following painful heel lance and venepuncture (14). Fetal brain blood circulation undergoes sudden changes during fetal painful procedures (15).
C Images Four-D images of the fetus have also been reported to show fetuses ‘crying’ after external stimuli (16) and having blink-startle reflex at 30 weeks of gestational age after an unpleasant stimulus (17). Infants delivered at 26–31 weeks show coordinated facial expressions in response to heel prick although these are immature compared to older infants (18).
D Hormons Transfusions performed in utero provoke an increase of stress hormones since 19 weeks of postgestational age, if performed through the skin, where nociceptive receptors are present, but not if performed through the umbilical cord, where these receptors are absent (19-21).
E Evidence of neonatal pain Newborns feel pain: this is a well established evidence. Thus, there is no reason to doubt that a fetus of the same level of development of a prematurely born baby can feel pain. Some fetuses arrive to the term of pregnancy (40 weeks), i.e. they are more developed of some newborns born at 25, 26 weeks, whose pain sensation is out of doubt and who receive analgesia for surgery.
4. Some objections
Some studies (22-24), object that these evidences cannot be considered evidences of pain, basing their objections upon two main arguments.
The first is the absence of cortical involvement in pain processing before 24 weeks GA; this would mean an absence of consciousness and, according with these authors, an absence of pain perception. Nevertheless, several studies (25) highlight the clinical evidence for perception mediated by subcortical centers (namely the thalamus): infants and children with hydranencephaly, despite total or near-total absence of the cortex, possess some form of discriminative awareness (26), and the subplate vicariates the definitive cortex in those critical development weeks.
The second argument is the supposed continuous state of fetal sleep throughout pregnancy, that would inhibit pain perception, even beyond the 24th week GA. Nonetheless, Van de Pas (27) described states F3 (calm wake) and F4 (active wake) up to 21% of daytime in term fetuses, and even the state F5 (crying) is described in a fetus (16). Moreover, a great difference exists between sedation and sleep: during pregnancy fetuses sleep, but sleep does not annihilate the possibility of experiencing pain.
5. The fetus as a patient: analgesia
Fetal surgery has recently made rapid progresses (1-5). Now it is possible to treat some mechanical anomalies before birth, and this in some cases has brought clear advantages to the babies, who have not to wait birth to be cured. Fetal surgery is used in fetuses with congenital diaphragmatic hernia, in whom lung growth is triggered by percutaneous tracheal occlusion. It can also be used to treat urinary obstructions. Many fetal interventions remain investigational, but randomised trials have established the role of in utero surgery for a number of conditions, making fetal surgery a clinical reality. Even non-lethal conditions, such as myelomeningocele repair, can be considered an indication (5).
During fetal surgery, the fetus undergoes several potentially painful procedures, and direct analgesics should be administered to him/her. Mother’s anesthesia is not sufficient to overcome pain during surgery (during C-sections performed with general mother’s anesthesia, babies are often born awake), then (28-30) direct analgesia is provided to the fetus.
A sufficient evidence exist to admit that during surgery fetuses from 20-22 weeks of gestational age undergo pain during potentially painful maneuvers. Some authors agree with this limit (31-33).
This evidence has some important legal consequences: in fact, some US States subordinate the possibility of legal abortion to the exclusion of the possibility of fetal pain. In early 2010, the Nebraska state legislature passed a new abortion restricting law asserting a new, compelling state interest in preventing fetal pain. Idaho law, passed during the 2011 Legislature, bans abortions once a fetus has reached 20 weeks on the belief that fetuses begin to feel pain at that stage. Idaho was one of five states along with Kansas, Alabama, Indiana and Oklahoma that enacted bans modeled after a fetal pain bill passed in Nebraska in 2010.
Being painful, does not add “per se” moral gravity to the voluntary abortion, that is always the deliberate suppression of a living prenatal baby. Nevertheless, it makes the injustice more evident.
7. Table 1
(weeks of gestational age)
Myelination (the formation of a sort of insulation of each nerve from the outer environment)
Substance P (a transmitter of pain impulse)
Connections between pain receptors and the thalamus (The thalamus is the structure where most nociceptive or pleasant stimuli are decoded)
Direct thalamocortical fibers (the fibers that connect the thalamus with the cortex)
Subplate (a waiting compartment for growing cortical afferents. Its cells are involved in the establishment of pioneering cortical efferent projections and transient fetal circuitry)
- Williams H. Questioning the rationale and conduct of the management of myelomeningocele study. Med Hypotheses. 2011 Apr 29. [Epub ahead of print]
- Hartmann KE, McPheeters ML, Chescheir NC, Gillam-Krakauer M, McKoy JN, Jerome R, Sathe NA, Meints L, Walsh WF. Evidence to Inform Decisions About Maternal-Fetal Surgery: Technical Brief. Obstet Gynecol. 2011May;117(5):1191-1204.
- Ruano R. Fetal surgery for severe lower urinary tract obstruction. Prenat Diagn. 2011 Mar 17. doi: 10.1002/pd.2736. [Epub ahead of print]
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- Simpson JL, Greene MF. Fetal surgery for myelomeningocele? New Engl Journal Med. 2011 Mar 17; 364(11):1076-7.
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- Kostovic I, Rakic P. Developmental history of the transient subplate zone in the visual and somatosensory cortex of the macaque monkey and human brain. J Comp Neurol. 1990;297:441-470.
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¿Cómo citar esta voz?
Sugerimos el siguiente modo de citar, que contiene los datos editoriales necesarios para la atribución de la obra a sus autores y su consulta, tal y como se encontraba en la red en el momento en que fue consultada:
Bellieni, Carlo, FETAL PAIN. NEW ADVANCES, en García, José Juan (director): Enciclopedia de Bioética.