Facial expressions of acute pain in 23-week fetus

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.

ASSESSMENT OF HUMAN FETUSES UNDERGOING ACUTE PAIN: VALIDATION OF THE FETAL-7 SCALE

Improvements in fetal ultrasound have allowed for the diagnosis and treatment of fetal diseases in the uterus, often though surgery. However, little attention has been drawn to the assessment of fetal pain. To address this gap, a fetal pain scoring system, known as the Fetal-7 scale, was developed. The present study is a full validation of the Fetal-7 scale. The validation involved two steps: i. four fetuses with indication of surgery were evaluated in three conditions perioperatively: acute pain, rest, and under loud sound stimulation. Facial expressions were assessed by 30 raters using screenshots from 4D high-definition ultrasound films; ii., assessment of sensitivity and specificity of the Fetal-7 scale in 54 healthy fetuses and two fetuses undergoing acute pain after preoperative anesthetic intramuscular injection. There was high internal consistency with Cronbach's alpha (α) of 0.99. Intra-rater reliability of the Fetal-7 scale (test-retest) calculated by intraclass correlation coefficient (ICC) was 0.95, and inter-rater reliability was 0.99. The scale accurately differentiated between healthy fetuses at rest and those experiencing acute pain (sensitivity of 100% and specificity of 94.4%). The Fetal-7 scale is a valid tool for assessing acute pain-related behavior in third trimester fetuses and may be of value in guiding analgesic procedures efficacy in these patients. Further research is warranted to explore the presence of post-operative pain in fetuses and its effects afterbirth. PERSPECTIVE: Recordings with three-dimension ultrasound of human fetuses undergoing pre-operative anesthetic injections revealed complex facial expressions during acute pain, similar to those collected in newborns. This study presented the validation process and cut-off value of the Fetal-7 scale, paving the way for the study of pain before birth in humans.

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.

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.