Perinatal data
| 82–85 cohort | 91–92 cohort | 99–00 cohort | P value | ||||
| Term-born, participated/eligible | 46/46 | 35/35 | 57/57 | − | |||
| EP-born, participated/eligible | 49/51 | 35/35 | 64/88 | − | |||
| Perinatal data of term-born and EP-born subjects | |||||||
| Birth weight in grams, mean (range) | |||||||
| Term-born | 3441 | (3000–4000) | 3564 | (3010–4000) | 3696 | (2990–4500) | 0.003 |
| EP-born | 1005 | (580–1480) | 933 | (570–1400) | 844 | (450–1250) | <0.001 |
| EP no BPD | 1047 | (580–1480) | 976 | (620–1400) | 862 | (450–1250) | 0.001 |
| EP BPD | 888 | (670–1080) | 851 | (570–1200) | 827 | (520–1100) | 0.39 |
| Maternal smoking during pregnancy, n (%) | |||||||
| Term-born | 10 | (22) | 9 | (26) | − | (26)* | 0.72 |
| EP-born | 22 | (48) | 13 | (38) | 15 | (25) | 0.06 |
| 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).