It is time for midwives and obstetricians to forget about the baroreflex in labor

On behalf of our coauthors, we would like to thank Lear and colleagues for their interest in our expert review, “Pathophysiological interpretation of fetal heart rate tracings in clinical practice.” We note that the authors have stated that we were “perpetuating the concept that the baroreflex makes a meaningful contribution to intrapartum fetal heart rate (FHR) decelerations.” This is far from the truth, because we had explicitly stated that “[a]lthough earlier animal experimental studies have suggested that fetal carotid baroreceptors played a role in these “quick” decelerations, recent animal studies have disputed the role of baroreceptors in the causation of these ‘quick’ decelerations. Some suggest that the predominant mechanism for such rapid and abrupt changes in the heart rate, followed by its rapid recovery is mediated through the peripheral chemoreflex and not the baroreflex.”1Jia Y.J. Ghi T. Pereira S. Gracia Perez-Bonfils A. Chandraharan E. Pathophysiological interpretation of fetal heart rate tracings in clinical practice.Am J Obstet Gynecol. 2023; 228: 622-644Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar Lear et al’s studies2Lear C.A. Kasai M. Booth L.C. et al.Peripheral chemoreflex control of fetal heart rate decelerations overwhelms the baroreflex during brief umbilical cord occlusions in fetal sheep.J Physiol. 2020; 598: 4523-4536Crossref PubMed Scopus (26) Google Scholar have shown that a hybrid origin of most fetal intrapartum decelerations seems likely, as the baroreflex was shown to trigger the deceleration in the first 3 to 4 seconds of the umbilical cord compression and the chemoreflex was shown to sustain the deceleration thereafter. The introduction of cardiotocography (CTG) technology into clinical practice without any previous randomized controlled trials and the lack of physiological knowledge regarding fetal compensatory responses resulted in several CTG guidelines focusing on the morphology of FHR decelerations. These reflex responses to reduce the myocardial workload were termed “early,” “variable,” “late,” “typical,” “atypical,” “complicated,” “uncomplicated,” “reassuring,” and “nonreassuring,” which had resulted in considerable inter- and intraobserver variabilities and an exponential increase in the unnecessary intrapartum operative interventions. In the physiological CTG interpretation, understanding the mechanisms behind FHR decelerations rather than labeling their type is emphasized. The authors would like to point out that the animal experiments, which used inflatable silicone occluders to completely occlude the umbilical cord, missed the reported initial increase in fetal blood volume with the onset of uterine contractions in human fetuses,3McNamara H. Johnson N. The effect of uterine contractions on fetal oxygen saturation.Br J Obstet Gynaecol. 1995; 102: 644-647Crossref PubMed Scopus (91) Google Scholar which may increase the blood pressure and stimulation of baroreceptors. Therefore, animal experiments may not reflect the complexity of human labor where changes occur at both the placental level and cord level during a contraction. In our opinion, it is time to stop arguing about the morphology or the receptors responsible for the decelerations. It is time to start determining the fetal response to stress and features of different types of hypoxia on the CTG trace to improve maternal and perinatal outcomes. It is time for midwives and obstetricians to forget about the baroreflex in laborAmerican Journal of Obstetrics & GynecologyPreviewWe read the review by Jia et al1 with interest but are surprised to see them perpetuate the concept that the baroreflex makes a meaningful contribution to intrapartum fetal heart rate (FHR) decelerations. It is of particular concern that they propose yet another non–evidence-based label for short variable decelerations. Full-Text PDF