Table 1.
Main characteristics of the studied mothers
(Mean values and standard deviations; numbers and percentages)
| Characteristics | n | % | |
|---|---|---|---|
| Age (years) | |||
| Mean | 31·0 | ||
| sd | 5·0 | ||
| Education level | |||
| Junior high/high school | 28 540 | 36·2 | |
| Higher professional school/vocational school/junior college | 32 767 | 41·6 | |
| University/graduate school | 17 200 | 21·8 | |
| Missing | 286 | 0·4 | |
| Smoking | |||
| Never | 46 062 | 58·5 | |
| Former | 28 673 | 36·4 | |
| Current | 3397 | 4·3 | |
| Missing | 661 | 0·8 | |
| Alcohol drinking | |||
| Never | 26 622 | 33·8 | |
| Former | 49 517 | 62·8 | |
| Current | 2123 | 2·7 | |
| Missing | 531 | 0·7 | |
| Parity | |||
| 0 | 31 219 | 39·6 | |
| 1 | 29 831 | 37·9 | |
| ≥2 | 15 887 | 20·2 | |
| Missing | 1856 | 2·4 | |
| Household annual income (million Japanese yen) | |||
| <2 | 4162 | 5·3 | |
| 2–<4 | 25 494 | 32·4 | |
| 4–<6 | 24 219 | 30·7 | |
| ≥6 | 19 472 | 24·7 | |
| Missing | 5446 | 6·9 | |
| Prepregnancy BMI (kg/m2) | |||
| <18·5 | 12 744 | 16·2 | |
| 18·5–<25 | 58 160 | 73·8 | |
| 25–<30 | 6126 | 7·8 | |
| ≥30 | 1763 | 2·2 | |
| Hyperthyroidism | |||
| Yes | 769 | 1·0 | |
| No | 77 591 | 98·5 | |
| Missing | 433 | 0·5 | |
| Hypothyroidism | |||
| Yes | 695 | 0·9 | |
| No | 77 665 | 98·6 | |
| Missing | 433 | 0·5 | |
| Folate supplement use | |||
| None | 45 747 | 58·1 | |
| Once/month | 1821 | 2·3 | |
| 2–3 times/month | 3972 | 5·0 | |
| 1–3 times/week | 6391 | 8·1 | |
| 4–6 times/week | 4348 | 5·5 | |
| Once/d | 15 320 | 19·4 | |
| ≥2 times/d | 983 | 1·2 | |
| Missing | 211 | 0·3 | |
| Offspring’s sex of current pregnancy | |||
| Male | 40 414 | 51·3 | |
| Female | 38 379 | 48·7 | |
| Gestational age of the offspring of current pregnancy (weeks) | |||
| Mean | 38·9 | ||
| sd | 1·5 | ||