Table 1

Perinatal data

82–85 cohort91–92 cohort99–00 cohortP value
Term-born, participated/eligible46/4635/3557/57
EP-born, participated/eligible49/5135/3564/88
Perinatal data of term-born and EP-born subjects
 Birth weight in grams, mean (range)
  EP no BPD1047(580–1480)976(620–1400)862(450–1250)0.001
  EP BPD888(670–1080)851(570–1200)827(520–1100)0.39
 Maternal smoking during pregnancy, n (%)
Perinatal data of the EP-born subjects
 Gestational age in weeks, mean (range)27.5(23–34)26.7(23–31)26.7(24–31)0.03
 SGA, n (%)9(18)5(14)23(36)0.03
 Birth weight Z score, mean (SD)−0.5(1.2)−0.3(0.9)−0.8(1.3)0.13
 Postnatal days with oxygen treatment, median (quartiles)†42(26–56)49(26–71)61(40–78)0.05
 Days on CPAP, median (quartiles)3(0–14)8(1–28)29(19–42)<0.001
 Ventilator days, median (quartiles)8(1–16)4(1–12)5(2–9)0.04
 BPD n (%)13(27)12(34)33(52)0.02
 Antenatal steroids, n (%)17(35)15(44)52(81)<0.001
 Surfactant, n (%)0(0)17(49)54(84)<0.001
 Postnatal steroids, n (%)4(8)10(29)20(31)0.01
 PDA closure, medical or surgical, n (%)13(27)17(49)14(22)0.02
  • Cohort differences were tested using Welch’s one-way ANOVA for continuous variables and Pearson’s χ2 test for categorical variables.

  • *Data not recorded for term-born from this cohort; the reported value represents percentage of smoking mothers of all births in the region, from the medical birth registry of Norway. The corresponding p value is based on comparison of the two earliest cohorts.

  • †Cohort differences were tested using Kruskall-Wallis test due to skewed data.

  • ANOVA, analysis of variance; BPD, bronchopulmonary dysplasia (supplemental oxygen or respiratory support at postmenstrual age ≥36 weeks); CPAP, continuous positive airway pressure; EP, subjects born extremely preterm or with extremely low birth weight (gestational age ≤28 weeks or birth weight ≤1000 g); PDA, persistent ductus arteriosus; SGA, small for gestational age (BW <10th percentile for GA according to Norwegian growth curves).