Table 4

Spirometry variables below the lower limit of normal at any time

Cohort82–85 cohort91–92 cohort99–00 cohort
Z-FEV1 below LLN at any time, n (%), p valueTerm-born (ref.)3(7)3(9)6(11)
EP no BPD10(28)0.014(17)0.317(23)0.13
EP BPD7(54)<0.0016(50)0.0028(24)0.08
Z-FVC below LLN at any time, n (%), p valueTerm-born (ref.)3(7)0(0)4(7)
EP no BPD8(22)0.042(9)0.081(3)0.46
EP BPD2(15)0.311(8)0.084(12)0.41
Z-FEV1/FVC below LLN at any time, n (%), p valueTerm-born (ref.)1(2)5(14)1(2)
EP no BPD8(22)0.0043(13)0.899(29)<0.001
EP BPD5(38)<0.0019(75)<0.00110(30)<0.001
Z-FEF25-75% below LLN at any time, n (%), p valueTerm-born (ref.)2(4)6(17)6(11)
EP no BPD11(31)0.0013(13)0.679(29)0.03
EP BPD7(54)<0.0019(75)<0.00112(36)0.003
Any variable below LLN at any time, n (%), p valueTerm-born (ref.)5(11)7(20)8(14)
EP no BPD17(47)<0.0016(26)0.5912(39)0.008
EP BPD9(69)<0.00110(83)<0.00115(45)<0.001
  • The presented data are the number (fraction) of subjects with at least one value ≤LLN at least one visit.

  • P value refers to comparisons between term-born and EP-born groups using Pearson’s χ2 test.

  • EP, subjects born extremely preterm or with extremely low birth weight (gestational age ≤28 weeks or birth weight ≤1000 g); FEF25–75%, forced expiratory flow at 25–75% of FVC; FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity; LLN, Lower limit of normal (z-score ≤ −1.645); ref., reference level.