Table 1

Characteristics of the study population

N*Mean (SD) or %
Child's characteristics
 Gestational age (weeks)448839.8 (1.2)
 Birth weight (kg)43883.3 (0.4)
 Weight at 3 months (kg)37395.8 (0.8)
 Weight at 6 months (kg)30867.6 (0.9)
 Weight at 12 months (kg)39469.7 (1.1)
 Weight at 18 months (kg)288311.2 (1.3)
 Sex
  Male230351.3%
  Female218948.7%
 Siblings
  Yes123727.5
  No325372.5
  Missing values2
 Wheezing from 6 to 18 months
  Yes77617.3%
  No371682.7%
 Lower respiratory tract infections†
  Yes91320.3%
  No357979.7%
Maternal characteristics
 Age (years)449233.6 (4.2)
 Pre-pregnancy BMI
  <18.53908.9%
  18.5–24.99316472.1%
  25+83319.0%
  Missing values105
 Nationality
  Italian429095.5%
  Other2024.5%
 Educational level‡
  Low1944.4%
  Medium146632.9%
  High279362.7%
  Missing values39
 Smoking during pregnancy
  Yes3477.8%
  No409292.2%
  Missing values53
 Smoking after delivery§
  Yes58813.2%
  No386986.8%
  Missing values35
 Asthma diagnosis
  Yes3508.0%
  No401592.0%
  Missing values127
  • *Total numbers may vary across variables due to missing values.

  • †Lower respiratory tract infections (bronchitis, bronchiolitis and pneumonia) between 6 and 18 months of age.

  • ‡Low—primary school or less; medium—secondary school; and high—university degree.

  • §Maternal active smoking in the first 18 months after delivery.

  • BMI, body mass index.