Histologic chorioamnionitis and fat mass accretion in infants born preterm.

Background: In utero insults such as chorioamnionitis are associated with adverse outcomes. This study aims to examine the association between chorioamnionitis and fat mass (FM) in very preterm infants.

Methods: We conducted a retrospective cohort study of mother-infant dyads born <32^6/7 weeks of gestation. Infant FM accretion was measured using air displacement plethysmography at term-equivalent age. Histological chorioamnionitis severity was staged based on placental pathology and included maternal/chorion-amnion inflammatory response (MIR) and fetal/umbilical cord inflammatory response (FIR). The association between chorioamnionitis severity and FM accretion was analyzed using linear regression models and mediation analyses.

Results: Among 375 mother-infant dyads analyzed, 104 (28%) dyads had MIR. FIR was found in 85 dyads with MIR (82%). Infants without MIR had lower FM in Kg and lower FM z scores than those with MIR (p = 0.0001). Infants with severe MIR had higher body fat percentages (Stage 3: 18% vs Stage 1: 14%, p < 0.0001). There were no significant differences in other anthropometric growth rates. Gestational age partially mediated this association (49%).

Conclusion: Severe histological chorioamnionitis is associated with greater FM accretion at term-equivalent age, independent of gestational age. Without long-term data, it remains unclear whether this early-onset effect is transient or persists into later childhood.

Impact statement: Chorioamnionitis is common in infants born preterm and is strongly associated with preterm birth. Infants born preterm exposed to chorioamnionitis have an increased risk of abnormal fat mass accretion at term equivalent age. Accounting for the severity of chorioamnionitis could improve the interpretation of body fat accretion in infants born preterm.