Hypoxic-ischemic encephalopathy following intrapartum asphyxia: is it avoidable?

Abstract

Background: The proportion of term hypoxic-ischemic encephalopathy arising during intrapartum fetal surveillance remains unclear. Moreover, recent Cochrane review and other studies emphasized the need for research on the impact of admission cardiotocography and highlighted the necessity for a definition of "avoidable perinatal brain injury".

Objective: To assess the impact of intrapartum asphyxia on neonatal hypoxic-ischemic encephalopathy occurrence and identify the proportion of cases that benefit from preventive measures.

Study design: This retrospective 20-year birth cohort study included admission and intrapartum cardiotocography recordings from spontaneous term (≥37 weeks of gestation) singleton deliveries at 7 maternity hospitals within the Helsinki University Hospital area, Finland, between 2005 and 2024. In newborns diagnosed with hypoxic-ischemic encephalopathy, cases following intrapartum asphyxia were identified by a normal cardiotocogram at admission, whereas antepartum exposure was indicated by an abnormal admission cardiotocogram. Cord blood gases, erythropoietin, and serum S100β concentrations were analyzed, and placentas underwent histopathological examination. Primary outcome was hypoxic-ischemic encephalopathy. Secondary outcome was fetal asphyxia, defined as the presence of severe or moderate acidemia.

Results: Among 317,126 term newborns, 314 cases of hypoxic-ischemic encephalopathy were identified. Admission cardiotocogram was normal in 141 (44.9%) and abnormal in 173 (55.1%). Of those with a normal admission cardiotocogram, severe acidemia (umbilical artery pH <7.00 and/or base excess ≤-12.0 mmol/L) evolved in 127/141 (90.1%) and moderate acidemia (umbilical artery pH 7.09-7.00 and base excess -10.0 to -11.9 mmol/L) in 11/141 (7.8%). Excluding cases with a perinatal sentinel event and timely deliveries, 70 cases (49.6%) remained in which hypoxic-ischemic encephalopathy presumably developed during labor and was considered potentially avoidable. These findings suggest that in 22.3% (70/314), preventive measures should have been implemented. Newborns with abnormal cardiotocograms had higher median umbilical blood erythropoietin concentrations than those with normal admission cardiotocograms (112 U/L, interquartile range 22-1130 vs 29 U/L, interquartile range 7-680, P<.001), indicating more chronic hypoxia.

Conclusion: Of term newborns with hypoxic-ischemic encephalopathy and normal admission cardiotocogram, 98% were attributable to intrapartum asphyxia. Our findings indicate that half of the cases of intrapartum hypoxic-ischemic encephalopathy with a normal admission cardiotocogram were potentially avoidable, suggesting that one-fifth of all cases could have benefited from preventive measures. The findings underscore the role of optimal intrapartum care in preventing hypoxic-ischemic encephalopathy.

Keywords: admission cardiotocography; avoidable perinatal brain injury; hypoxic-ischemic encephalopathy; intrapartum asphyxia.