Risk factors for neonatal hypoxic ischemic encephalopathy and therapeutic hypothermia: a matched case-control study

Peripartum asphyxia is one of the main causes of neonatal morbidity and mortality. In moderate and severe cases of asphyxia, a condition called hypoxic-ischemic encephalopathy (HIE) and associated permanent neurological morbidities may follow. Due to the multifactorial etiology of asphyxia, it may be difficult prevent, but in term neonates, therapeutic cooling can be used to prevent or reduce permanent brain damage. The aim of this study was to assess the significance of different antenatal and delivery related risk factors for moderate and severe HIE and the need for therapeutic hypothermia.

We conducted a retrospective matched case-control study in Helsinki University area hospitals during 2013-2017. Newborn singletons with moderate or severe HIE and the need for therapeutic hypothermia were included. They were identified from the hospital database using ICD-codes P91.00, P91.01 and P91.02. For every newborn with the need for therapeutic hypothermia the consecutive term singleton newborn matched by gender, fetal presentation, delivery hospital, and the mode of delivery was selected as a control. Odds ratios (OR) between obstetric and delivery risk factors and the development of HIE were calculated.

Eighty-eight cases with matched controls met the inclusion criteria during the study period. Maternal and infant characteristics among cases and controls were similar, but smoking was more common among cases (aOR 1.46, CI 1.14-1.64, p = 0.003). The incidence of preeclampsia, diabetes and intrauterine growth restriction in groups was equal. Induction of labour (aOR 3.08, CI 1.18-8.05, p = 0.02) and obstetric emergencies (aOR 3.51, CI 1.28-9.60, p = 0.015) were more common in the case group. No difference was detected in the duration of the second stage of labour or the delivery analgesia.

Smoking, induction of labour and any obstetric emergency, especially shoulder dystocia, increase the risk for HIE and need for therapeutic hypothermia. The decisions upon induction of labour need to be carefully weighed, since maternal smoking and obstetric emergencies can hardly be controlled by the clinician.