Table 1.
Baseline characteristics of children by breastfeeding groups in the longitudinal survey of babies in the 21st century (nbaseline=43 383)
| Exclusively formula fed (n=2597) | Partially breast fed |
Exclusively breast fed (n=9521) | |||
|---|---|---|---|---|---|
| 1–2 M (n=8592) | 3–5 M (n=8625) | 6–7 M (n=14 048) | |||
| Biological factor | |||||
| Birth weight, g | 3064 | 3059 | 3075 | 3088 | 3111 |
| (SD) | (404) | (388) | (377) | (370) | (361) |
| Female | 47% | 48% | 50% | 47% | 50% |
| Parity | |||||
| 1 (no older siblings) | 49% | 49% | 52% | 54% | 41% |
| 2 | 35% | 37% | 35% | 33% | 42% |
| 3 | 12% | 12% | 10% | 10% | 15% |
| ≥4 | 4% | 3% | 2% | 2% | 3% |
| Maternal age at delivery | |||||
| <25 | 17% | 20% | 16% | 10% | 11% |
| 25.1–29.9 | 36% | 39% | 40% | 38% | 39% |
| 30–34.9 | 31% | 30% | 32% | 38% | 39% |
| ≥35 | 16% | 11% | 12% | 14% | 12% |
| Socioeconomic factor | |||||
| Maternal educational attainment* | |||||
| High school or less | 63% | 58% | 47% | 37% | 37% |
| Two-year college or vocational school | 31% | 34% | 41% | 45% | 45% |
| Four-year college or higher | 6% | 8% | 12% | 18% | 18% |
| Maternal smoking status* | |||||
| Non-smoker | 69% | 68% | 79% | 90% | 92% |
| Light smoker | 17% | 18% | 14% | 8% | 6% |
| Heavy smoker | 14% | 14% | 7% | 2% | 2% |
| Marital status | |||||
| Not married | 2% | 2% | 1% | 1% | 1% |
| Family income* | 522 | 511 | 554 | 594 | 576 |
| In 10 000 yen (SD) | (558) | (318) | (391) | (366) | (353) |
| Region of birth | |||||
| Hokkaido | 4% | 4% | 4% | 3% | 4% |
| Tohoku | 12% | 11% | 8% | 6% | 5% |
| Kanto | 38% | 33% | 33% | 32% | 27% |
| Chubu | 16% | 17% | 17% | 19% | 19% |
| Kinki | 14% | 17% | 18% | 19% | 20% |
| Chugoku | 4% | 5% | 6% | 6% | 8% |
| Shikoku | 4% | 4% | 3% | 2% | 3% |
| Kyushu/Okinawa | 9% | 9% | 10% | 13% | 14% |
*There were 3030 missing cases for maternal educational attainment, 281 missing cases for maternal smoking status and 2767 missing cases for family income.