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 Rhöse S, Heinis AM, Vandenbussche F, van Drongelen J, van Dillen J. 2014. Inter- and intra-observer agreement of non-reassuring cardiotocography analysis and subsequent clinical management. Acta Obstetricia et Gynecologica Scandinavica 93:596–602.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]; Reif et al. 2016 Reif P, Schott S, Boyon C, Richter J, Kavšek G, Timoh KN, et al. 2016. Does knowledge of fetal outcome influence the interpretation of intrapartum cardiotocography and subsequent clinical management? A multicentre European study. BJOG 123:2208–2217.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]), even amongst ‘experts’ (Hruban et al. 2015 Hruban L, Spilka J, Chudáček V, Janků P, Huptych M, Burša M, et al. 2015. Agreement on intrapartum cardiotocogram recordings between expert obstetricians. Journal of Evaluation in Clinical Practice 21:694–702.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). Furthermore, it has been shown that CTG traces do not reliably predict neonatal encephalopathy (Spencer et al. 1997 Spencer JA, Badawi N, Burton P, Keogh J, Pemberton P, Stanley F. 1997. The intrapartum CTG prior to neonatal encephalopathy at term: a case-control study. British Journal of Obstetrics and Gynaecology 104:25–28.[Crossref], [PubMed] , [Google Scholar]).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.