Impact of chorionicity and histological chorioamnionitis on neurodevelopment and mortality in extremely preterm twins

Histological chorioamnionitis (HCAM) is associated with adverse neurodevelopmental outcomes; however, its role in extremely preterm twin pregnancies (<28 weeks of gestation), particularly in relation to chorionicity, is unclear.

To evaluate the association between HCAM severity and neurodevelopmental outcomes at 3 years old in extremely preterm twins, focusing on the modifying effect of chorionicity.

Utilizing data from the Neonatal Research Network of Japan (2004-2020), this retrospective cohort study included twins born at <28 weeks' gestation and birth weight < 1500 g. HCAM severity was classified based on Blanc's criteria. Primary outcomes were cerebral palsy (CP) and developmental quotient (DQ) < 70 at 3 years old, assessed using the Kyoto Scale of Psychological Development. Secondary outcomes included death before neonatal intensive care unit (NICU) discharge and a composite outcome of death, including CP or DQ < 70. Multivariate logistic regression was performed adjusting for confounders and including interaction terms.

Among 1249 infants, HCAM severity was not significantly associated with CP or DQ < 70 in monochorionic diamniotic (MD) or dichorionic diamniotic (DD) twins. MD twins exhibited a significantly higher mortality risk than DD twins (adjusted odds ratio: 1.73; 95 % confidence intervals: 1.22-2.46). Moreover, significant interaction between HCAM and chorionicity was not observed for mortality.

In this large, multicenter cohort of extremely preterm twins, HCAM was not associated with adverse neurodevelopmental outcomes or early mortality. However, monochorionic status was independently associated with increased NICU mortality, highlighting the predominant role of chorionicity in twin pregnancy-related outcomes.