Spirometry phenotypes at 8 years in children born extremely preterm or with extremely low birth weight.

Introduction: Preterm birth is associated with poor expiratory airflow, but spirometry phenotypes are not well-described.

Objectives: To characterise abnormal spirometry phenotypes at age 8 years in children born either extremely preterm (EP; <28 weeks' gestation) or extremely low birth weight (ELBW; <1000 g birth weight), and to describe the early-life (perinatal and early growth) variables associated with each phenotype.

Methods: Participants comprised survivors born EP/ELBW in Victoria, Australia, in three eras (1991-1992, 1997 and 2005) and contemporaneous term-born controls with spirometry data at 8 years. Abnormal spirometry phenotypes included: prematurity-associated obstructive lung disease (POLD), prematurity-associated preserved ratio of impaired spirometry (pPRISm) and prematurity-associated dysanapsis (pDysanapsis). Lung volumes measured by plethysmography and early-life variables were compared between each abnormal and the normal spirometry phenotype.

Results: Overall, 29% (156/544) of children born EP/ELBW had an abnormal spirometry phenotype compared with 9% (47/524) term-born controls (OR 4.06, 95% CI 2.85 to 5.79; p<0.001). Compared with children born EP/ELBW with normal spirometry (71%), children born EP/ELBW with pPRISm (11%) had reduced total lung volume. Both POLD (8%) and pPRISm phenotypes showed evidence of air trapping. Bronchopulmonary dysplasia was associated with both POLD and pPRISm. Lower gestational age and poorer weight gain between birth and 2 years were associated with pPRISm. No early life variables were associated with pDysanapsis (9%).

Conclusion: Over one-quarter of children born EP/ELBW have abnormal spirometry phenotypes. Abnormal spirometry phenotypes differ in their associations with perinatal or early growth variables.