Table 1. Baseline characteristics of children by maternal age group in the 2001 cohort of the Longitudinal Survey of Babies in 21st Century (nbaseline = 47,015).
| <25.0 | 25.0–29.9 | 30.0–34.9 | 35.0–39.9 | > = 40.0 | p-valueb | |
|---|---|---|---|---|---|---|
| (n = 6,327) | (n = 18,065) | (n = 16,561) | (n = 5,406) | (n = 656) | ||
| Biological factors | ||||||
| Female | 48.8% | 47.5% | 48.3% | 48.4% | 46.7% | p = 0.36 |
| Birthweight in gramsa | 3026 | 3029 | 3042 | 3046 | 2996 | p<0.01 |
| (SD) | 414 | 415 | 440 | 472 | 500 | |
| Low birthweight | 8.4% | 8.1% | 8.6% | 9.4% | 13.3% | p<0.01 |
| Preterm birth a | 4.8% | 4.5% | 5.3% | 6.2% | 9.5% | p<0.01 |
| Parity | p<0.01 | |||||
| 1 | 76.4% | 58.3% | 35.9% | 27.3% | 30.3% | |
| 2 | 21.3% | 34.0% | 44.0% | 39.6% | 32.8% | |
| 3> = | 2.3% | 7.8% | 20.2% | 33.2% | 36.9% | |
| Socioeconomic factors | ||||||
| Maternal educational attainmenta | p<0.01 | |||||
| High school or less | 67.4% | 43.8% | 39.8% | 40.6% | 42.3% | |
| Two years of college | 29.1% | 43.1% | 43.5% | 42.1% | 40.0% | |
| or vocational school | ||||||
| Four years of college or | 3.6% | 13.1% | 16.8% | 17.4% | 17.6% | |
| higher | ||||||
| Paternal educational attainmenta | p<0.01 | |||||
| High school or less | 71.3% | 49.8% | 41.2% | 40.2% | 45.2% | |
| Two years of college | 15.2% | 17.1% | 15.4% | 13.0% | 10.8% | |
| or vocational school | ||||||
| Four years of college or | 13.6% | 33.2% | 43.4% | 44.8% | 44.0% | |
| higher | ||||||
| Maternal employment statusa | p<0.01 | |||||
| Employed full-time | 37.0% | 36.2% | 27.5% | 26.4% | 25.4% | |
| Maternal smoking statusa | p<0.01 | |||||
| Smoker | 34.5% | 18.5% | 12.2% | 11.1% | 13.1% | |
| Paternal agea | 25.8 | 30.2 | 34.1 | 38.3 | 42.4 | p<0.01 |
| (SD) | 4.5 | 4 | 4.1 | 4.7 | 5.1 | |
| Family incomea | 378 | 526 | 616 | 687 | 713 | p<0.01 |
| in JPY10,000 (SD) | 380 | 317 | 358 | 461 | 550 | |
| at Wave 1 |
a 14 missing cases for birthweight, 36 missing cases for preterm birth, 298 missing cases for maternal educational attainment, 792 missing cases for paternal educational attainment, 442 missing cases for maternal employment status, 278 missing cases for maternal smoking status, 612 missing cases for paternal age, and 3194 missing cases for family income.
b We assessed the associations between all biological and socioeconomic factors and maternal age using chi square tests and ANOVA.