Fetal Pain: The Science Behind Why It Is the Medical Standard of Care

An Evidence-Based Discussion of Fetal Pain and Stress

BACKGROUND

The concept of fetal pain results from procedures conducted without anesthesia in preterm newborns and fetuses, which indicate that it is possible to examine fetal pain based on stress hormone, metabolic, and behavioral changes. Anatomical and physiological data suggest that fetuses become capable of processing nociceptive stimuli around midgestation, although the associated changes in fetal brain development remain unclear. What constitutes fetal pain remains controversial in the light of the definition of pain adopted by the International Association for the Study of Pain (IASP), which posits pain as an "unpleasant sensory and emotional experience."

SUMMARY

Here, we examine the notion that human fetuses cannot "experience" pain and potential implications of this claim. We highlight the key scientific evidence related to fetal pain, including clinical studies on pain in fetuses and preterm newborns. We argue that consistent patterns of stress hormones, metabolic changes, body movements, hemodynamic changes, and pain-related facial expressions in fetuses exposed to invasive procedures overcome the need for subjective proof of pain as articulated in the IASP definition. No study to date has conclusively proven the absence of fetal pain beyond the age of viability.

KEY MESSAGES

Based on the current evidence, we propose that all fetuses receive anesthesia regardless of the invasive procedures being performed to guarantee the least possible pain and physiological, behavioral, or hormonal responses without exposing the mother or her baby to unnecessary complications.

Difficulties in Adaptation of the Mother and Newborn via Cesarean Section versus Natural Birth-A Narrative Review

Birth is a physiological act that is part of the morpho-functional economy of the maternal body. Each stage in the act of birth has a predetermined pathway that is neurohormonally induced and morpho-functionally established through specific and characteristic adaptations. Like maternity, childbirth also has an important impact on the maternal body as a biological structure and psycho-emotional behavior. Cesarean section performed at the request of the mother with no medical underlying conditions besides the prolonged hospitalization risk can also cause breathing problems in children, delayed breastfeeding, and possible complications in a future pregnancy. Vaginal birth remains the path of choice for a physiological evolution pregnancy. Although erroneously considered safe and easy today, cesarean section delivery must remain an emergency procedure or a procedure recommended for pregnancies where birth is a risk to the mother and to the child, as cesarean section itself is a risk factor for negative outcomes for both mother and baby. This review summarizes the impact that both cesarean section and natural birth have on mother and newborn in their attempt to adapt to postpartum events and extrauterine life.

The fetal pain paradox

Controversy exists as to when conscious pain perception in the fetus may begin. According to the hypothesis of cortical necessity, thalamocortical connections, which do not form until after 24-28 weeks gestation, are necessary for conscious pain perception. However, anesthesiologists and neonatologists treat age-matched neonates as both conscious and pain-capable due to observable and measurable behavioral, hormonal, and physiologic indicators of pain. In preterm infants, these multimodal indicators of pain are uncontroversial, and their presence, despite occurring prior to functional thalamocortical connections, has guided the use of analgesics in neonatology and fetal surgery for decades. However, some medical groups state that below 24 weeks gestation, there is no pain capacity. Thus, a paradox exists in the disparate acknowledgment of pain capability in overlapping patient populations. Brain networks vary by age. During the first and second trimesters, the cortical subplate, a unique structure that is present only during fetal and early neonatal development, forms the first cortical network. In the third trimester, the cortical plate assumes this function. According to the subplate modulation hypothesis, a network of connections to the subplate and subcortical structures is sufficient to facilitate conscious pain perception in the fetus and the preterm neonate prior to 24 weeks gestation. Therefore, similar to other fetal and neonatal systems that have a transitional phase (i.e., circulatory system), there is now strong evidence for transitional developmental phases of fetal and neonatal pain circuitry.

A Comprehensive Assessment of The Eight Vital Signs

The term “vital sign” has been assigned to various phenomena with the presumptive intent to emphasize their importance in health care resulting in the emergence of eight vital signs with multiple designations and overlapping terms. This review developed a case definition for vital signs and identified and described the fifth through eighth vital signs. PubMed/Medline, Google and biographical databases were searched using the individual Medical Subject Headings (MeSH) terms, vital sign and fifth, vital sign and sixth, vital sign and seventh, and vital sign eighth. The search was limited to human clinical studies written in English literature from 1957 up until November 30, 2021. Excluded were articles containing the term vital sign if used alone without the qualifier fifth, sixth, seventh, or eighth or about temperature, blood pressure, pulse, and respiratory rate. One hundred ninety-six articles (122 for the fifth vital sign, 71 for the sixth vital sign, two for the seventh vital sign, and one for the eighth vital sign) constituted the final dataset. The vital signs consisted of 35 terms, classified into 17 categories compromising 186 unique papers for each primary authored article with redundant numbered vital signs for glucose, weight, body mass index, and medication compliance. Eleven terms have been named the fifth vital sign, 25 the sixth vital sign, three the seventh, and one as the eighth vital sign. There are four time-honored vital signs based on the case definition, and they represent an objective bedside measurement obtained noninvasively that is essential for life. Based on this case definition, pulse oximetry qualifies as the fifth while end-tidal CO2 and cardiac output as the sixth. Thus, these terms have been misappropriated 31 times. Although important to emphasize in patient care, the remainder are not vital signs and should not be construed in this manner.

Fetal Pain in the First Trimester

Fetal pain perception has important implications for fetal surgery, as well as for abortion. Current neuroscientific evidence indicates the possibility of fetal pain perception during the first trimester (<14 weeks gestation). Evidence for this conclusion is based on the following findings: (1) the neural pathways for pain perception via the cortical subplate are present as early as 12 weeks gestation, and via the thalamus as early as 7–8 weeks gestation; (2) the cortex is not necessary for pain to be experienced; (3) consciousness is mediated by subcortical structures, such as the thalamus and brainstem, which begin to develop during the first trimester; (4) the neurochemicals in utero do not cause fetal unconsciousness; and (5) the use of fetal analgesia suppresses the hormonal, physiologic, and behavioral responses to pain, avoiding the potential for both short- and long-term sequelae. As the medical evidence has shifted in acknowledging fetal pain perception prior to viability, there has been a gradual change in the fetal pain debate, from disputing the existence of fetal pain to debating the significance of fetal pain. The presence of fetal pain creates tension in the practice of medicine with respect to beneficence and nonmaleficence.