The human nervous system continuously processes a potentially overwhelming stream of signals from bodily senses, which induces uncertainty. To reduce this uncertainty, the brain transforms sensory input into a reliable perception of the world. According to the Bayesian hypothesis of perception, based on probabilistic estimation, conscious perception is shaped by both the current state of sensory information and by past experiences, associative learning, stored memories, and beliefs. This framework is particularly relevant for explaining the phenomenon of pain, including individual differences in pain perception and response.
The focus of the present work is pain during childbirth, representing a major acute pain event. Pain during childbirth is a complex and unique experience with both sensory and emotional components, embedded within a defined physiological process. A key concept of the Bayesian model related to pain perception is the placebo phenomenon, which offers a compelling explanation for the analgesic placebo response.
The overarching aim of this study is to evaluate whether the Bayesian model can account for changes in pain perception during labor following open placebo administration, as well as the involvement of expectations and personality traits.
The study will be conducted at Hillel-Yaffe Medical Center, with the participation of 120 pregnant women. The research will be divided into two stages. The first stage will occur during the prenatal period, while participants are in a pain-free state. During this stage, questionnaires will be completed to assess expectations and personality traits, and the Focused Analgesia Selection Test (FAST) will be administered to evaluate within-subject variability in pain intensity. The second stage will take place during labor and will involve an open placebo intervention, during which pain levels and analgesic consumption will be monitored.
Pregnant women with one fetus who are after 24th week onwards.
Without contraindications for analgesia at birth.
Without contraindications for vaginal birth.
Women in obstetric emergencies, including intrauterine death, suspected placental separation, uterine rupture, placental opening
Elective cesarean section
Receiving psychiatric treatment.
Parallel
Open Label Placebo
BehavioralAny woman who arrive to the labor room is connected to fluids (Hartman's solution), as part of routine care. The study intervention (open placebo) is based on injection of placebo into an infusion bag accompanied by a verbal suggustion. The placebo is 5 ml NaCl 0.9%.
Pain intensity on a 0-10 Numerical Pain Scale (NPS)
Pain assessment will be performed by using the unidimensional Numerical Pain Scale (NPS) by asking the patient to range the pain, subjectively, from her point of view, from none (0) to a worst imaginable pain (10). Pain intensity will be assessed once in 60 minutes for the duration of the labor. Since each labor duration is difrent, the primary outcome would be the levels of pain during the labor process. Those intensities over time will be compared bewteen the two study arms. In addition, in additional analyses, pain intensities will be compared for each labor phase, seperatly.
Within-subject variability of pain reports
The Focused Analgesia Selection Test (FAST) procedure will be used to assess the within-subject variability of pain reports. The FAST includes exposure to several thermal noxious stimuli, administrated repeatedly at different intensities, which will be delivered to the ventral surface of the non-dominant arm (Medoc® Thermal Sensory Analyzer II with a thermodin size of 30 \* 30 mm). Pain intensity ratings are obtained from the participant after each stimulus on a 0-100 numerical rating scale (NRS) ranging from 0 ("no pain") to 100 ("worst pain imaginable"). Stimuli will be triggered automatically every 20 seconds. Relationship between stimulus intensities and pain reports are calculated (R2 and ICC) to assess the magnitude of variability observed.
Assessment of expectations from the treatment
Patients' expectations toward the treatment will be assessed by the EXPECT questionnaire (short version), which includes four items. Three items relate to the respondent's realistic expectations from the treatment, and one item relates to his/her hopes and wishes regarding the treatment. The intent of the question about hope is to increase respondents' focus on answering the 3 expectations questions in terms of their realistic expectations as opposed to their hopes for treatment outcomes. Alpha Cronbach for the short form of the EXPECT questionnaire is 0.89 according to the authors' report.
Fear of childbirth
Severe fear of childbirth will be measured by the Wijma Delivery Expectancy/Experience Questionnaire (W-DEQ), 27 Version A. The W-DEQ consists of 33 items, all of which are rated on a 6-point Likert scale, ranging from 0 to 5. Sum scores range from 0 to 165, with higher scores reflecting a greater degree of fear of childbirth. As suggested in the literature, participants with sum scores ≥85 were defined as suffering from severe fear of childbirth. Internal consistency of the W-DEQ in our study sample was high, with Cronbach's α = .92. The questionnaire has been translated and back-translated by Yael Benyamini and her research team.
Suggestibility
To assess the suggestibility, we are going to use short suggestibility scale (SSS) from the Multidimensional Iowa Suggestibility questionnaire, a scale of multidimensional measure of suggestibility with two companion constructs, with 95 items in total. In the original study by Kotov and colleagues the SSS scale reliability was .89 and correlated with the total suggestibility index obtained with the Multidimensional Iowa Suggestibility Scale. The SSS is composed by 34 21 items, and calculated by the sum of each item, and higher scores represent higher suggestibility trait.
Anxiety
Anxiety will be measured by the Generalized Anxiety Disorder Questionnaire (GAD-7). The GAD-7 is a seven items self-report scale to assess the frequency of symptoms of anxiety with a 4-point Likert-scale ranging from 0 (not at all) to 3 (nearly every day). Items are summed to yield a total score ranging from 0 to 21, with higher scores indicating more anxiety symptoms. The GAD-7 has good sensitivity and specificity for specific anxiety disorders. The GAD- 7 severity cut point is 10 for moderate and severe anxiety. In this study, we used the sum of the GAD-7 as a continuous variable as well as indication for anxiety disorder using the validate cut-off of ≥10. Cronbach's alpha coefficient for the current study was α = 0.92.
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Roi Treister
Lead sponsor
University of Haifa
Sponsor institution
Hillel Yaffe Medical Center
Collaborator
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