Table 1.
Characteristics of the study population
(Numbers and percentages; mean values and standard deviations)
| n | % | |
|---|---|---|
| n | 10 543 | |
| Maternal characteristics | ||
| Age (years) | ||
| Mean | 32·1 | |
| sd | 4·8 | |
| Height (cm) | ||
| Mean | 158·5 | |
| sd | 5·4 | |
| Pre-pregnancy weight (kg) | ||
| Mean | 53·9 | |
| sd | 9·1 | |
| Pre-pregnancy BMI* | ||
| <18·5 (kg/m2) | 1453 | 13·8 |
| 18·5–24·9 (kg/m2) | 7710 | 73·1 |
| ≥25·0 (kg/m2) | 1224 | 11·6 |
| Missing | 156 | 1·5 |
| Parity | ||
| Never | 4802 | 45·5 |
| One or more | 5722 | 54·3 |
| Missing | 19 | 0·2 |
| Educational attainment | ||
| High school graduate or less | 2901 | 27·5 |
| Junior college or vocational college graduate | 3703 | 35·1 |
| University graduate or above | 2809 | 26·6 |
| Others | 22 | 0·2 |
| Missing | 1108 | 10·5 |
| Household income | ||
| <4 000 000 (Japanese Yen/year) | 3443 | 32·7 |
| 4 000 000–5 999 999 (Japanese Yen/year) | 3409 | 32·3 |
| ≥6 000 000 (Japanese Yen/year) | 3287 | 31·2 |
| Missing | 404 | 3·8 |
| Cigarette smoking | ||
| Never | 6690 | 63·5 |
| Stopped before pregnancy | 2496 | 23·7 |
| Stopped after pregnancy | 1167 | 11·1 |
| Current | 162 | 1·5 |
| Missing | 28 | 0·3 |
| Alcohol consumption | ||
| Never | 4774 | 45·3 |
| Former | 3592 | 34·1 |
| Current | 2151 | 20·4 |
| Missing | 26 | 0·2 |
| Folic acid supplementation during pregnancy | ||
| Yes | 6265 | 59·4 |
| No | 4265 | 40·5 |
| Missing | 13 | 0·1 |
| Personal PDD history | ||
| Yes | 4 | 0·0 |
| No | 9492 | 90·0 |
| Missing | 1047 | 9·9 |
| Fertility treatment | ||
| Yes | 1238 | 11·7 |
| No | 9280 | 88·0 |
| Missing | 25 | 0·2 |
| HG from conception to early pregnancy | ||
| No | 1483 | 14·1 |
| Just nausea | 4793 | 45·5 |
| Vomiting, but was able to eat | 3197 | 30·3 |
| Vomiting, and was unable to eat | 1055 | 10·0 |
| Missing | 15 | 0·1 |
| HG from early to mid-pregnancy | ||
| No | 7039 | 66·8 |
| Just nausea | 2414 | 22·9 |
| Vomiting, but was able to eat | 985 | 9·3 |
| Vomiting, and was unable to eat | 85 | 0·8 |
| Missing | 20 | 0·2 |
| Paternal characteristics | ||
| Personal PDD history | ||
| Yes | 5 | 0·0 |
| No | 9491 | 90·0 |
| Missing | 1047 | 9·9 |
| Infant characteristics | ||
| Infant sex | ||
| Male | 5468 | 51·9 |
| Female | 5065 | 48·0 |
| Missing | 10 | 0·1 |
| Birth season | ||
| Spring (March–May) | 2655 | 25·2 |
| Summer (June–August) | 2516 | 23·9 |
| Autumn (September–November) | 2776 | 26·3 |
| Winter (December–February) | 2596 | 24·6 |
| Breast-feeding duration | ||
| <6 (months) | 1864 | 17·7 |
| ≥6 (months) | 7056 | 66·9 |
| Missing | 1623 | 15·4 |
| ASQ-3 | ||
| Failed one domain | 1004 | 9·5 |
| Failed two domains | 284 | 2·7 |
| Failed three domains | 154 | 1·5 |
| Failed four domains | 62 | 0·6 |
| Failed five domains | 68 | 0·6 |
| Failed one or more of the domains | 1572 | 14·9 |
ASQ-3, Ages & Stages Questionnaires, Third Edition; HG, hyperemesis gravidarum; PDD, pervasive developmental disorder.
*
Pre-pregnancy BMI was calculated by dividing the pre-pregnancy weight (kg) by the square of maternal height (m2).