Correcting standardized expiratory flows for prematurity in ex‐preterm survivors—Is it necessary?

Objective To determine the effect of correcting for prematurity on standardized values for expiratory flow rates for participants from 5 years through to 70 years of age. Methods In a theoretical model we assumed starting values for expiratory flows that were expected to give ranges within ±2 SD. Keeping expiratory flows, ethnicity and height constant, we then determined how z scores varied between 5 and 16.9 years, and, with two different fixed values for height and expiratory flows, between 16 and 70 years of ages, for both sexes. In a clinical example, we compared expiratory flows with age both corrected and uncorrected for prematurity between 144 survivors born extremely preterm and 141 term‐born controls at both 8 and 18 years of age. Results In the theoretical models, z scores mostly declined through childhood until the late teenage years, and then began to rise through later life. The maximum difference in z‐scores between corrected and uncorrected scores for a participant born 4 months’ preterm would occur in the early teenage years, and for the forced vital capacity would be approximately −0.09 SD wider. In the clinical example not correcting for prematurity resulted in a maximum gap between preterm and term cohorts 0.06 SD wider for the forced vital capacity at 8 years than if age was corrected for prematurity. Conclusions Correction for prematurity is not necessary in clinical practice, and is probably not required for research in studies of respiratory airflow through childhood or adulthood.