Transfer of Respiratory Syncytial Virus Prefusion F Protein Antibody in Low Birthweight Infants.

Background: Respiratory syncytial virus (RSV)-associated lower respiratory tract infection contributes significantly to morbidity/mortality worldwide in low birthweight (LBW) infants (<2500 g). Studies have demonstrated decreased maternal immunoglobulin G (IgG) transfer of various antibodies to LBW infants. We aimed to evaluate naturally acquired RSV anti-prefusion F protein (anti-preF) antibody transfer in pregnancies with LBW versus normal birthweight (NBW) infants.

Methods: In this cohort study conducted among pregnant individuals and their infants, we tested paired maternal and singleton infant cord samples for RSV anti-preF IgG via an electrochemiluminescence immunoassay, using linear regression to evaluate associations between LBW and anti-preF IgG. Covariates included seasonality, insurance, small-for-gestational-age birthweight, and gestational age at delivery.

Results: We tested maternal/cord RSV anti-preF IgG from 54 and 110 pregnancies with LBW and NBW infants, respectively. Of LBW infants, 22 (40.7%) were born both preterm and with small-for-gestational-age birthweight. The median (interquartile range) gestational age at delivery and birthweight were 34.0 (31.7-37.1) weeks and 1902 (1393-2276) g for LBW infants versus 39.1 (38.3-39.9) weeks and 3323 (3109-3565) g for NBW infants (both < .001). In unadjusted comparisons, preterm infants had significantly lower cord anti-preF IgG levels and cord-maternal IgG ratios compared with full-term infants, while LBW infants had significantly lower cord-maternal IgG ratios than NBW infants (all < .01). After adjustment for covariates, there was no difference in cord-maternal IgG ratios (β =-0.29 [95% confidence interval, -.63 to .05]) between LBW and NBW infants.

Conclusions: We documented robust transfer of maternal RSV anti-preF IgG in pregnancies with both LBW and NBW infants. Further studies are needed to assess immune protection in at-risk infants.