Recognition of Chorioamnionitis on the Cardiotocograph (CTG): The role of the “Chorio Duck Score”

Abstract

Chorioamnionitis refers to the inflammation of the chorion and amnion by the bacteria and their toxins as well as by the inflammatory cytokines. Therefore, it is a fetal disease with the bacteria, their toxins as well as the fetal immunological responses involving inflammatory cytokines (interleukins, interferons, and tumour necrosis factor-alpha) exerting their detrimental effects within the fetal compartment (i.e., amniotic fluid, fetal membranes, the placenta, and fetal tissues and organs). The vast majority of fetal inflammation occurs as a result of an ascending infection (i.e., entry of the bacteria from the maternal genital tract through the cervix). Therefore, maternal signs (tachycardia and pyrexia) may not be observed until the late stages of the disease. Cardiotocograph (CTG) trace was introduced into clinical practice in the 1960s as a tool to timely recognise ongoing fetal hypoxic stress so that immediate action could be taken to avoid hypoxic ischaemic encephalopathy (HIE) and/ or intrapartum hypoxia-related perinatal deaths. Unfortunately, the CTG was introduced into clinical practice without any prior randomised controlled trials, which resulted in panicking and reacting to the observed morphology of fetal heart rate decelerations, which reflect an ongoing fetal compensatory response to reduce the myocardial workload. A sudden and reflex reduction of the heart rate in response to ongoing intermittent hypoxic stress (i.e., repetitive compression of the umbilical cord or interruptions in uteroplacental oxygenation due to uterine contractions) would ensure a reduction in myocardial oxygen demand and maintenance of aerobic metabolism to avoid the onset of anaerobic metabolism and production of lactic acid within the myocardium. Lack of understanding of fetal compensatory responses resulted in the illogical approach of grouping arbitrary features into different categories and then randomly combining them to classify the CTG traces into “Normal, Suspicious, and Pathological”. The same parameters were used in fetuses with chorioamnionitis with an alternative, inflammatory pathway of neurological injury. The international consensus guidelines of physiological interpretation of CTG produced by 44 CTG experts from 14 countries in 2018 ensured a paradigm shift and recommended classification of CTG traces based on the type of fetal hypoxia and fetal response to stress, by applying the knowledge of fetal physiology whilst interpreting CTG traces. During the last 5 years, research has highlighted CTG features in fetal neuro-inflammation, which include an absence of fetal heart rate cycling, the ZigZag Pattern, and sinusoidal patterns. The proposed “Chorio Duck Score” is a scoring system based on recently published scientific evidence on CTG features in subclinical and clinical chorioamnionitis to enable timely diagnosis of fetal systemic inflammatory response syndrome (FIRS). This will help avoid the continuation of super-imposed hypoxic stress (i.e., progressive increasing frequency, duration, and strength of uterine contractions) on the background fetal inflammation, to prevent fetal neurological injury.