Table 1.
Maternal and child characteristics
| n = 4951 | |
|---|---|
| Maternal characteristics | |
| Age, y | 30.7 (4.9) |
| Body mass index at enrolment (kg/m2)a | 23.7 (18.7‐35.7) |
| Educational level, higher (%) | 51.0 (2525) |
| History of asthma or atopy, yes (%) | 39.0 (1932) |
| Psychiatric symptoms (GSI)a | 0.17 (0.0‐1.26) |
| Parity, nullipara (%) | 57.9 (2869) |
| Smoking during pregnancy, yes (%) | 30.3 (1502) |
| Pet keeping, yes (%) | 41.9 (2072) |
| Damp patches or mould in house, yes (%) | 16.2 (804) |
| Folate concentration in early pregnancy, nmol/La | 18.2 (4.1‐51.2) |
| Mid‐gestational blood sampling season (%) | |
| Spring | 31.0 (1537) |
| Summer | 22.2 (1097) |
| Autumn | 23.9 (1182) |
| Winter | 22.9 (1135) |
| 25‐Hydroxyvitamin D concentration in mid‐gestation (nmol/L)a | 53.0 (8.1‐122.5) |
| Severely deficient (%) | 20.1 (905) |
| Deficient (%) | 26.1 (1178) |
| Sufficient (%) | 53.8 (2424) |
| Child characteristics | |
| Female sex (%) | 50.6 (2504) |
| Gestational age at birth (weeks)a | 40.1 (35.9‐42.3) |
| Birth weight (grams) | 3449 (550) |
| Ethnic background (%) | |
| Dutch and Western | 70.1 (3471) |
| Turkish and Moroccan | 11.3 (561) |
| African | 10.8 (537) |
| Asian | 7.7 (383) |
| Ever breastfeeding, yes (%) | 88.3 (4372) |
| Day care attendance first year, yes (%) | 61.6 (3049) |
| At birth blood sampling season (%) | |
| Spring | 24.1 (1192) |
| Summer | 26.7 (1324) |
| Autumn | 27.2 (1349) |
| Winter | 21.9 (1086) |
| 25‐Hydroxyvitamin D concentration at birth (nmol/L)a | 30.7 (5.3‐82.7) |
| Severely deficient (%) | 40.2 (1320) |
| Deficient (%) | 37.4 (1229) |
| Sufficient (%) | 22.4 (735) |
| 25‐Hydroxyvitamin D concentration at the age of 6 y (nmol/L)a | 65.6 (19.1‐134.8) |
| FEV1 (z‐score) | 0.17 (0.98) |
| FVC (z‐score) | 0.21 (0.94) |
| FEV1/FVC (z‐score) | −0.09 (0.95) |
| FEF75 (z‐score) | 0.05 (0.92) |
| Current asthma at the age of 10 y, yes (%) | 5.7 (226) |
| Inhalant allergic sensitization at the age of 10 y, yes (%) | 32.9 (1131) |
| Physician‐diagnosed inhalant allergy at the age of 10 y, yes (%) | 13.3 (369) |
Values are means (SD), aMedians (2.5‐97.5th percentile) or valid percentages (absolute numbers), based on imputed data. Data on 25‐hydroxyvitamin D in mid‐gestation (n = 444), at birth (n = 1667), at the age of 6 y (n = 2142), and forced expiratory volume in 1 s (FEV1) (n = 752), forced vital capacity (FVC) (n = 752), FEV1/FVC ratio (n = 752), forced expiratory flow after exhaling 75% of FVC (FEF75) (n = 752), current asthma (n = 1001), inhalant allergic sensitization (n = 1512) and physician‐diagnosed inhalant allergy (n = 2173) was not imputed.