Table 2 Demographic data of nulliparous and parous women (n = 56 101) in the Norwegian mother and child cohort study, 1999-2008

Mean (SD) age at delivery (y)

28.4 (4.3)

31.8 (4.1)

<0.001

Mean (SD) prepregnant BMI (kg/m²)

23.7 (4.1)

24.2 (4.2)

<0.001

Prepregnant BMI categories (%)

  < 18.5

3.2

2.5

  18.5-25

68.7

64.1

  25-30

20.0

23.7

<0.001

  >30

8.1

9.7

  Class 1

6.0

7.2

  Class II

1.6

1.9

  Class III

0.5

0.6

Mean (SD) height (m)

1.68 (0.06)

1.68 (0.06)

ns

Education (%)

  High school or less

27.5

35.8

  College 3 years

43.9

41.0

  Masters and higher

26.5

21.2

<0.001

  Missing

2.1

2.0

Smoking in pregnancy (%)

  Not smoking

90.5

88.3

  Occasional smoking

3.0

2.7

  Daily smoking

4.7

6.5

<0.001

  Missing

1.8

2.5

Mean (SD) gestational weight gain (kg)

15.5 (6.1)

14.7 (5.9)

<0.001

Mean (SD) postpartum weight retention at:

6 months (kg)

1.2 (5.0)

1.3 (4.5)

0.016

18 months (kg)

n = 19604 ^§

n = 16593 ^§

2.1 (5.7)

0.8 (5.1)

<0.001