Table 1.
Characteristics for girls and boys of the Fit Futures cohort at birth and four ages up to 18–20 years, The Tromsø Study, Fit Futures, observed cases*
| Characteristics | Girls | Boys | p Value† | ||||
| n | Mean/% | (SD) | n | Mean/% | (SD) | ||
| Birth | |||||||
| Birth weight (g) | 443 | 3455.0 | (576.7) | 470 | 3601.0 | (590.0) | <0.001 |
| Birth length (cm) | 419 | 49.4 | (2.3) | 454 | 50.2 | (2.3) | <0.001 |
| Gestational age (weeks) | 393 | 39.7 | (1.8) | 430 | 39.6 | (2.1) | 0.176 |
| Preterm birth (before GA week 37) | 15 | 3.8% | 23 | 5.4% | 0.292 | ||
| Ponderal index (kg/m3) | 419 | 28.73 | (2.81) | 454 | 28.45 | (2.75) | 0.141 |
| Body mass index (kg/m2) | 419 | 14.19 | (1.49) | 454 | 14.28 | (1.52) | 0.338 |
| Birth weight SDS‡ | 443 | −0.58 | (1.74) | 470 | −0.24 | (1.32) | 0.001 |
| Body mass index SDS‡ | 419 | 0.06 | (1.05) | 454 | −0.02 | (1.04) | 0.265 |
| Birth weight group: | 443 | 470 | 0.015 | ||||
| Low birth weight (<2500 g) | 20 | 4.5% | 17 | 3.6% | |||
| Normal birth weight (2500–4500 g) | 412 | 93.0% | 423 | 90.0% | |||
| High birth weight (≥4500 g) | 11 | 2.5% | 30 | 6.4% | |||
| Size for gestational age: | 443 | 470 | 0.554 | ||||
| Small for gestational age | 49 | 11.1% | 46 | 9.8% | |||
| Appropriate for gestational age | 356 | 80.4% | 375 | 79.8% | |||
| Large for gestational age | 38 | 8.6% | 49 | 10.4% | |||
| Maternal age at birth | 443 | 28.4 | (5.3) | 441 | 28.1 | (5.3) | 0.995 |
| 2–4 years of age | |||||||
| Age (years) | 328 | 2.6 | (0.4) | 350 | 2.6 | (0.4) | 0.952 |
| Height (cm) | 328 | 91.2 | (4.6) | 350 | 92.7 | (4.7) | <0.001 |
| Weight (kg) | 328 | 13.5 | (1.7) | 350 | 14.1 | (1.8) | <0.001 |
| Body mass index (kg/m2) | 328 | 16.17 | (1.39) | 350 | 16.37 | (1.30) | 0.053 |
| Weight SDS‡ | 328 | −0.12 | (1.11) | 350 | 0.16 | (1.16) | 0.001 |
| Body mass index SDS‡ | 328 | −0.04 | (1.17) | 350 | −0.07 | (1.07) | 0.217 |
| 5–7 years of age | |||||||
| Age (years) | 354 | 6.0 | (0.4) | 384 | 6.1 | (0.4) | 0.253 |
| Height (cm) | 354 | 116.7 | (5.3) | 384 | 118.3 | (5.3) | <0.001 |
| Weight (kg) | 352 | 21.8 | (3.8) | 384 | 22.2 | (3.5) | 0.143 |
| Body mass index (kg/m2) | 352 | 15.96 | (2.04) | 384 | 15.82 | (1.74) | 0.304 |
| Weight SDS‡ | 352 | 0.0004 | (1.10) | 384 | 0.11 | (1.02) | 0.162 |
| Body mass index SDS‡ | 352 | −0.06 | (1.10) | 384 | −0.03 | (0.98) | 0.616 |
| 15–17 years of age | |||||||
| Age (years) | 469 | 16.6 | (0.4) | 492 | 16.6 | (0.4) | 0.325 |
| Height (cm) | 467 | 164.9 | (6.5) | 492 | 176.9 | (6.7) | <0.001 |
| Weight (kg) | 467 | 60.9 | (11.5) | 492 | 70.2 | (14.4) | <0.001 |
| Body mass index (kg/m2) | 467 | 22.39 | (3.96) | 492 | 22.38 | (4.17) | 0.952 |
| Pubertal maturation, §girls: | 464 | – | – | – | |||
| Early (<12.5 years) | 147 | 31.7% | |||||
| Intermediate (12.5–13.9 years) | 212 | 45.7% | |||||
| Late (≥14.0 years) | 105 | 22.6% | |||||
| Pubertal maturation, §boys: | – | – | – | 387 | |||
| Barely started (PDS 2.0–2.9) | 69 | 17.8% | |||||
| Underway (PDS 3.0–3.9) | 285 | 73.6% | |||||
| Completed (PDS 4.0) | 33 | 8.5% | |||||
| 18–20 years of age | |||||||
| Age (years) | 363 | 18.6 | (0.4) | 296 | 18.7 | (0.3) | 0.105 |
| Height (cm) | 363 | 165.7 | (6.5) | 296 | 179.1 | (6.5) | <0.001 |
| Weight (kg) | 363 | 63.2 | (12.0) | 296 | 75.2 | (14.6) | <0.001 |
| Body mass index (kg/m2) | 363 | 23.02 | (4.22) | 296 | 23.42 | (4.18) | 0.228 |
*In observed data n is varying from 659 to 961.
†p Value for sex difference was obtained by t-test or χ2 test.
‡SDS, SD scores according to Norwegian reference data.23
§Pubertal maturation is based on age of menarche in girls and according to Pubertal Development Scale (PDS) in boys; total score of four items of secondary sexual characteristics on a scale from 1 to 4 (sum of total score divided by 4). None had a score <2.0 in total score.25
GA, gestational age.