Table 1. Characteristics of the study participants (n = 74,240).
| Number | (%) | |
| Maternal history of allergy | ||
| Yes | 35,841 | (48.5) |
| No | 38,057 | (51.5) |
| Maternal age at pregnancy, years | ||
| <25 | 8,114 | (10.9) |
| ≥25 and <30 | 21,356 | (28.8) |
| ≥30 and <35 | 26,294 | (35.4) |
| ≥35 | 18,476 | (24.9) |
| Household income, million JPY/year | ||
| <4 | 26,353 | (35.5) |
| ≥4 to <6 | 35,045 | (47.2) |
| ≥6 | 7,873 | (10.6) |
| Unknown | 4,969 | (6.7) |
| Mode of delivery | ||
| Caesarean section | 14,508 | (19.6) |
| Vaginal | 59,417 | (80.4) |
| Birth weight, g | ||
| <2,500 | 6,621 | (8.9) |
| ≥2,500 | 67,448 | (91.1) |
| Child’s sex | ||
| Male | 37,974 | (51.2) |
| Female | 36,266 | (48.9) |
| Older siblings | ||
| Yes | 39,456 | (53.4) |
| No | 34,442 | (46.6) |
| Duration of exclusive breast-feeding | ||
| <6 months | 44,215 | (59.6) |
| At least 6 months | 30,025 | (40.4) |
| Passive smoking during pregnancy | ||
| Yes | 14,813 | (20.2) |
| No | 58,491 | (79.8) |
| Doctor diagnosed allergy | ||
| Infantile eczema | 3,086 | (4.2) |
| Mother’s peanut intake during pregnancy | ||
| At least once a week | 3,688 | (5.1) |
| 1–3 times a month | 13,753 | (19.0) |
| Less than once a month | 55,095 | (76.0) |
| Peanut introduction status at age 1 year | ||
| ≤6 months | 79 | (0.1) |
| 7–8 months | 440 | (0.6) |
| 9–10 months | 1,154 | (1.6) |
| 11–12 months | 1,693 | (2.3) |
| Intake after 13 months | 367 | (0.5) |
| Not ingested | 70,507 | (95.0) |
JPY, Japanese yen.