Table 1 Characteristics of the sample by sex

Parental rated ADHD-symptoms

490

9.5

5.0

403

8.4

4.7

*

Body size

At birth

   Weight, kg

490

3.4

0.8

403

3.3

0.7

*

   Length, cm

490

49.6

3.6

403

48.7

3.2

*

   Head circumference, cm

490

35.0

2.2

403

34.3

2.1

*

   BMI, kg/m²

490

13.5

1.8

403

13.5

1.8

At 5 months

   Weight, kg

482

7.6

0.9

394

7.0

0.9

*

   Length, cm

478

66.5

2.3

388

64.5

2.2

*

   Head circumference, cm

480

43.6

1.2

391

42.3

1.1

*

   BMI, kg/m²

476

17.2

1.5

388

16.8

1.5

*

At 20 months

   Weight, kg

457

12.1

1.4

376

11.4

1.4

*

   Height, cm

444

84.6

3.1

369

83.2

3.2

*

   Head circumference, cm

459

49.4

1.4

381

48.1

1.2

*

   BMI, kg/m²

440

16.8

1.4

369

16.4

1.3

*

At 56 months

   Weight, kg

482

18.5

2.6

393

17.8

2.7

*

   Height, cm

470

108.6

4.4

390

107.3

4.6

*

   Head circumference, cm

476

52.3

1.5

392

51.0

1.3

*

   BMI, kg/m²

469

15.6

1.5

387

15.4

1.5

*

Covariates

Gestational age, weeks

490

38.4

2.8

403

38.7

2.6

Admission to neonatal ward (n, %)

490

341

69.6

403

251

62.3

*

Multiple pregnancy (n, %)

490

21

4.3

403

21

5.2

Maternal smoking during pregnancy (n, %)

490

403

   > 10 cigarettes/day

27

5.5

25

6.2

   1-10 cigarettes/day

82

16.7

71

17.6

   None

381

77.8

307

76.2

Mother's

   Height, cm

490

164.4

5.4

403

164.3

5.5

   Age, Years

490

29.4

5.1

403

29.4

5.0

Parental education (n, %)

490

403

   I

58

11.8

48

11.9

   II

171

34.9

154

38.2

   III

151

30.8

107

26.6

   IV

110

22.4

94

23.3

Breast fed (yes: n, %)

490

457

93.3

403

378

93.8