Labouring on decelerations: the fetal peripheral chemoreflex wins.

Abstract

Recordings of fetal heart rate provide the clinician with the only non‐invasive tool to continuously monitor fetal wellbeing during labour. By far, the most debated component of fetal heart rate monitoring during labour is the significance of fetal heart rate decelerations, which almost invariably occur in association with uterine contractions. Over the years, proposed possible triggers for these reductions in fetal heart rate have included fetal head compression, baroreflexes, chemoreflexes, Bezold–Jarisch reflexes and/or myocardial depression. In this issue of The Journal of Physiology, Lear et al. (2016) propose that a unified understanding of the physiology underlying intrapartum fetal heart decelerations is critical to improve their interpretation. The review reminds us that normal labour is associated with intermittent interruptions of uteroplacental gas exchange, such that ‘technically’ all babies experience some sort of asphyxia to a certain extent during labour. Although intrapartum fetal asphyxia is a term that is often avoided clinically, as it conjures thoughts of injury, it is a biochemical reality and it is useful for clinicians to understand the parameters underlying it. Reviewing and evaluating the available literature, Lear and colleagues suggest that, on balance, typical intrapartum decelerations are most likely the result of transient episodes of fetal hypoxia or fetal asphyxia and the consequent activation of the fetal peripheral chemoreflex response.