Table 1

Description of study population characteristics

VariablesnChildren eligible at birth
(n=1175)
nStudy population (n=620)
Male sex, n (%)1172591 (50.3)620323 (52.1)
Age at assessment (years.), mean (SD)8474.5 (0.16)6114.5 (0.2)
Height at assessment (cm), mean (SD)845106.2 (4.4)611106.2 (4.3)
Weight at assessment (kg), mean (SD)84618.3 (2.6)61118.4 (2.7)
Ethnic background, n (%)1165616
 White1118 (96.0)600 (97.4)
 Others47 (4.0)16 (2.6)
Birth weight, mean (SD)11633272.2 (447.5)6183266.4 (426.9)
Preterm (<37 weeks), yes n (%)116340 (3.4)61317 (2.8)
Siblings at birth, yes n (%)1175511 (43.5)620254 (41.0)
Day-care attendance, yes n (%)1046404 (38.6)603251 (41.6)
Maternal age at birth, mean (SD)117430.8 (4.0)61931.1 (3.7)
Parity1173618
 0648 (55.2)358 (57.9)
 1+525 (44.8)260 (42.1)
Maternal education level, n (%)1170617
 Primary or less247 (21.1)117 (19.0)
 Secondary452 (38.6)226 (36.6)
 University471 (40.3)274 (44.4)
Maternal social class, n (%)1175620
 I+II (high)295 (25.1)177 (28.6)
 III (mid)336 (28.6)194 (31.3)
 IV+V (low)544 (46.3)249 (40.1)
Maternal prepregnancy BMI, (kg/m2) n (%)1175620
 <18.555 (4.7)31 (5.0)
 18.5–25846 (72.0)455 (73.4)
 25–30197 (16.8)94 (15.2)
 >3077 (6.5)40 (6.5)
Maternal smoking in pregnancy, yes n (%)1141162 (14.2)60485 (14.1)
Father smoking in pregnancy, yes n (%)1144399 (34.9)606204 (33.7)
ETS
 0–14 months, yes n (%)1041155 (14.9)59891 (15.2)
 36–48 months, yes n (%)865408 (47.2)608288 (47.4)
Maternal allergic history*, yes n (%)1174333 (28.4)619178 (28.8)
Father allergic history*, yes n (%)1174279 (23.8)619160 (25.8)
Predominant breastfeeding (wks), n (%)1044589
 0202 (19.4)105 (17.8)
 >0–16337 (32.3)199 (33.8)
 16–24386 (37.0)213 (36.2)
 >24119 (11.4)72 (12.2)
Type of cooker in the home at 14 months, n (%)1145607
 Gas (natural gas or butane)424 (37.0)224 (36.9)
 Electric708 (61.8)375 (61.8)
 Others13 (1.1)8 (1.3)
Pets at home at 14 months, yes n (%)1045260 (24.9)602156 (25.9)
Dampness at home at 14 months, yes n (%)104789 (8.5)60343 (7.1)
LRTI from birth to 14 months, yes n (%)1127415 (36.8)620250 (40.3)
Wheezing from birth to 14 months, yes n (%)1128381 (33.8)620225 (36.3)
Current† wheezing at 4 years, yes n (%)871155 (17.8)613121 (19.7)
Medication use for wheezing at 4 years, yes n (%)841100 (11.9)59679 (13.3)
Current‡ asthma at 4 years, yes n (%)836116 (13.9)59292 (15.5)
Allergic status at age 4 years*, yes n (%)802202 (25.2)569147 (25.8)
  • *Suffering from allergic asthma, atopic dermatitis, eczema or allergic rhinitis.

  • †During the last 12 months.

  • ‡Doctor-diagnosis of asthma or medication use for wheezing at 4 years of age.

  • BMI, Body Mass Index; ETS, environmental tobacco smoke; LRTI, lower respiratory tract infections.