Recognition of chronic hypoxia and pre-existing foetal injury on the cardiotocograph (CTG): Urgent need to think beyond the guidelines

Abstract

Chronic utero-placental insufficiency may result in progressive hypoxia culminating in fetal decompensation and acidosis and this is termed 'chronic' or 'long-standing' hypoxia. It is essential to recognise the features of chronic hypoxia on the CTG trace so as to institute timely and appropriate action. The current guidelines may not capture a fetus who starts labour already compromised or limited in its ability to compensate for hypoxic or mechanical stresses during labour. The aim of this short review is to explore the CTG features that allow the clinician to recognise a fetus who may present with an antenatal insult such as chronic hypoxia, anaemia, infection, fetal arrhythmias and preexisting non-hypoxic brain injury.

Keywords: CTG monitoring; Cardiotocography; Chronic hypoxia; Fetal anaemia; Fetal stroke.

Fig. 1.

CTG trace showing chronic hypoxia. Note the high baseline, reduced variability and shallow decelerations. Apparent increase in variability seen during vaginal examination (artifact) should not be mistaken for improvement in variability.

Fig. 2.

Pathophysiology of chronic hypoxia.

Fig. 3.

Atypical sinusoidal pattern in foetal-maternal haemorrhage. Note saw-tooth pattern.

Fig. 4.

Pseudosinusoidal pattern. Note change to normal variability.

Fig. 5.

Abnormal foetal heart rate patterns in foetal arrhythmia. Note abrupt change in baseline foetal heart rate.

Fig. 6.

CTG trace in a foetus who has sustained a pre-existing brain injury: foetal stroke.