Table 1—

Perinatal and other potential risk factors by sex

MalesFemalesTotal
Subjects n7628061,568
Age yrs20.3±0.920.4±0.920.3±0.9
Mother smoked during pregnancy355 (47.7)§413 (52.4)768 (50.1)
First-born372 (48.8)420 (52.1)792 (50.5)
Birthweight g3383±591*3222±5523300 (576)
Height at birth cm506±28*498±24502 (26)
Maternal age yrs26.4±4.526.0±4.326.2 (4.4)
Low maternal age (<20 yrs)34 (4.5)*21 (2.6)55 (3.5)
Gestational age weeks median (range)40 (28–44)40 (29–44)40 (28–44)
Breastfeeding#63 (8.8)80 (10.5)143 (9.6)
Breastfeeding125 (17.4)144 (18.8)269 (18.1)
Bottle feeding, exclusively531 (73.9)541 (70.7)1072 (72.2)
Severe respiratory tract infection+125 (16.8)*87 (11.0)212 (13.8)
 Requiring doctor's consultation119 (16.1)*78 (9.9)197 (12.9)
 Requiring hospitalisation22 (3.0)19 (2.5)41 (2.7)
Current smoking280 (37.0)278 (35.0)558 (36.0)
Parent with asthma106 (13.9)§141 (17.5)247 (15.8)
Parent with allergy366 (48.0)*445 (55.2)811 (51.7)
  • Data are presented as mean±sd, n (%) or median (range)

  • #: exclusively for at least 2 weeks

  • : breast feeding with additional feeding

  • +: in the first year of life

  • Significant difference between males and females (tested by Chi-squared test or t-test)

  • *: p<0.05

  • §p<0.10