P2.G136: Placental Pathologic Lesions Associated with Severity of Neonatal Hypoxic-Ischemic Encephalopathy (HIE)

Background: Placental lesions are associated with worse outcomes in some neonatal pathologies, but their association with the severity of neonatal hypoxic-ischemic encephalopathy (HIE) has not been well described.

Methods: This retrospective study included neonates born at ≥36 weeks diagnosed with HIE between January 2012 and November 2022. The cohort was divided into mild and moderate-severe HIE based on Sarnat score. Placental histologic diagnoses were made using standard definitions as defined by the Amsterdam Placental Workshop Group Consensus Statement. Placental pathologies were classified into acute inflammation with attention to stages and grades of maternal and fetal inflammatory responses (MIR and FIR, respectively), maternal vascular malperfusion (MVM), fetal vascular malperfusion (FVM), villitis of unknown etiology, and other lesions. Chi-square analysis and Fisher’s exact test were used to compare rates of placental pathologies between mild and moderate-severe HIE groups.

Results: Out of 394 neonates ≥36 weeks’ gestation diagnosed with HIE, 172 had mild HIE and received supportive care, while 180 had moderate to severe HIE and underwent therapeutic hypothermia. 42 patients were excluded due to a lack of clinical information regarding the primary outcome. FIR was more closely associated with moderate to severe HIE than mild HIE (53% vs. 38%, P< 0.01). FIR stage ≥2 occurred in 81% and FIR grade 2 in 15% of those with moderate to severe HIE, compared to 34% and 3%, respectively, in mild HIE. MIR was diagnosed in more placentas from the moderate to severe HIE group (58% vs. 47%, P=0.04) with higher stage and grade MIR in patients with moderate to severe HIE (86% with MIR stage ≥2 and 19% with MIR grade 2). High-grade (patchy/diffuse) chronic villitis was more prevalent in the moderate to severe HIE group (18% vs. 8%, P< 0.01). One subcategory of MVM – placental thrombi – was more commonly diagnosed in the moderate to severe HIE group (18% vs. 9%, P=0.02). Ongoing longitudinal follow-up data is being collected.

Conclusion: There is a higher prevalence of acute placental inflammation (both FIR and MIR) as well as chronic inflammation in neonates with moderate to severe HIE compared to those with mild HIE. The role of placental inflammation in the etiology of HIE warrants further exploration.