Subtle Alterations of Tidal Breathing Variables in Healthy Late Preterm Neonates at Term-Equivalent Age

Late-preterm birth is associated with increased respiratory morbidity, but tidal breathing at term-equivalent age remains incompletely characterized. We hypothesized that healthy late-preterm neonates would differ from term neonates, with the between-group difference in t_PTEF/t_E designated as the primary outcome.

In this prospective cross-sectional study, 60 healthy late-preterm and 60 term neonates underwent tidal breathing analysis (MasterScreen PAED) at term-equivalent age (40 weeks' postmenstrual age) during natural quiet sleep without sedation.

Late-preterm neonates had lower t_PTEF/t_E (27.4 ± 7.0% vs. 31.2 ± 6.9%; Benjamini-Hochberg-adjusted p = 0.028; Cohen's d = 0.544) and V_PTEF/V_E [28.6 (25.1-31.0)% vs. 32.1 (27.3-35.5)%; adjusted p = 0.028; Cliff's δ = 0.304] than term neonates. Respiratory rate was higher (53.2 ± 9.1 vs. 49.6 ± 9.5 breaths/min), but not significant after correction (adjusted p = 0.126). No other tidal breathing variables differed significantly after correction. In the primary multivariable model, each additional week of exact gestational age was associated with a 1.18-percentage-point increase in t_PTEF/t_E after adjustment for sex, body weight, and crown-heel length (B = 1.182; 95% CI, 0.540-1.823; β = 0.323; p < 0.001). When postnatal age replaced gestational age, the association was inverse (B = -0.167/day; 95% CI, -0.263 to -0.071; β = -0.306; p < 0.001).

At term-equivalent age, healthy late-preterm neonates had modestly lower t_PTFEF/t_E and V_PTEF/V_E than term neonates. These findings may reflect subtle maturational differences in expiratory flow dynamics associated with late-preterm birth.