Types of intrapartum hypoxia on the cardiotocograph (CTG): do they have any relationship with the type of brain injury in the MRI scan in term babies?

Electronic foetal monitoring using cardiotocography is aimed at the timely recognition and management of foetal hypoxia. The primary objective of this study was to examine whether a relationship exists between the types of foetal hypoxia (acute, subacute, evolving, chronic), as identified on cardiotocography and the nature of hypoxic ischaemic encephalopathy, as observed on MRI scans after birth. We conducted a retrospective study of 16 babies born (out of 52,187 births) at St George's Hospital in London during 2006-2017 with a postnatal diagnosis of HIE. Of the 16 babies, only 11 had both MRI scans and CTG traces available. Of those, 9 showed evidence of intrapartum hypoxia on CTG, but only 6 demonstrated evidence of HIE on MRI. Those with acute hypoxia showed abnormalities in the basal ganglia and thalami. A gradually evolving hypoxia or subacute hypoxia was associated with lesions in myelination and cerebral cortex.Impact StatementWhat is already known on this subject? It has been reported that inter-observer agreement for CTG interpretation is low (30%) when pattern recognition based guidelines are used (Rhöse et al. 2014; Reif et al. 2016), even amongst 'experts' (Hruban et al. 2015). Furthermore, it has been shown that CTG traces do not reliably predict neonatal encephalopathy (Spencer et al. 1997).What do the results of this study add? Our study indicates that if 'types of intrapartum hypoxia' are used for interpretation, then inter-observer agreement increases to 81%, from the reported 30% when traces are classified into 'normal, suspicious and pathological' using guidelines based on 'pattern recognition'. Furthermore, our study shows a good correlation between the type of intrapartum hypoxia observed on CTG trace and the nature of injury observed on the MRI.What are the implications of these findings for clinical practise and/or further research? Improving inter-observer agreement of CTGs with the use of pattern recognition in combination with the good correlation to MRI scan findings ultimately leads to better management and post-natal outcomes. This is evidenced by the fact that after the introduction of physiology-based CTG interpretation and mandatory competency testing on CTG interpretation for all staff in 2010, St. George's Maternity Unit has half the nationally reported rate of cerebral palsy.

The relationship of asphyxia in the mature fetus to long-term neurologic function.

Asphyxia may occur before or during labor in the preterm or term fetus. The development of neuropathologic lesions depends on the degree and duration of the asphyxia. Anoxia may occur, but because of the short duration of the fetal response, it usually will cause the death of the fetus. The common mechanism leading to neuropathologic lesions in the fetus is a significant degree of hypoxia present for a particular period of time. Antepartum asphyxia will cause such lesions and deficits in children. What is missing are measures to establish the prevalence of antepartum asphyxia in a large population and the epidemiologic studies to determine the association between the asphyxia so documented and the deficits in surviving children. The prevalence of intrapartum fetal asphyxia is of the order of 2%. Most of these children will have no evidence of brain damage. The key is the fetal cardiovascular compensatory response that maintains cerebral blood flow and oxygen metabolism. This compensatory phase, subject to the severity of the hypoxia, may continue for several hours. In the clinical setting during labor, this provides the "window of opportunity" when a specific blood gas and acid-base diagnosis can be made, and with appropriate intervention, brain damage can be avoided. However, if the hypoxia persists, a threshold will be reached when fetal cardiovascular decompensation will occur. The compromised cerebral oxygen metabolism will result in brain damage and deficits in the children who survive. The threshold at which brain damage may occur is when the acidosis is severe (pH, < 7.0). At this time, systemic hypotension may occur.(ABSTRACT TRUNCATED AT 250 WORDS)

Foetal hypoxia--an anaesthetist's approach to classification and prevention.

Nearly one third of perinatal deaths are due to hypoxia occurring during pregnancy and labour. Many factors contribute to foetal hypoxia and in order to group these into orderly categories a classification of hypoxia, which is familiar to anaesthetists, has been applied to the maternal and foetal circulations. This theoretical approach forms a logical guide to our understanding the cause, prevention and treatment of foetal hypoxia.