Table 1.
Characteristics of mothers and infants who were included in the final analytic sample (n = 259) and those who were not included (n = 252).
| The final analytic sample (n = 259) | The participants who were not included (n = 252) | P a | |
|---|---|---|---|
| Characteristic | No. (%) | ||
| Maternal characteristics | |||
| Age (years)b | 31.3 ± 4.9 | 30.2 ± 4.7 | 0.01 |
| Education level (years) | 0.03 | ||
| ≤12 | 101 (39.0) | 124 (49.2) | |
| >12 | 158 (61.0) | 128 (50.8) | |
| Economic status: annual income (yen) | 0.04 | ||
| < 3,000,000 | 43 (16.6) | 51 (20.5) | |
| 3,000,000–5,000,000 | 120 (46.3) | 132 (53.0) | |
| >5,000,000 | 96 (37.1) | 66 (26.5) | |
| Missing | 0 (0) | 3 (1.2) | |
| Worked during pregnancy | 30 (11.6) | 25 (9.9) | 0.64 |
| Smoked during pregnancy | 32 (12.4) | 56 (22.2) | <0.01 |
| Alcohol intake during pregnancy | 78 (30.1) | 77 (30.6) | 0.99 |
| Fish intake during pregnancy | |||
| Inshore fish | 0.50 | ||
| ≤2 times/month; rarely/never | 146 (56.4) | 137 (54.4) | |
| 1–2 times/week | 100 (38.6) | 96 (38.1) | |
| 3+ times/week | 13 (5.0) | 19 (7.5) | |
| Deep-sea fish | 0.05 | ||
| ≤2 times/month; rarely/never | 125 (48.3) | 109 (43.3) | |
| 1–2 times/week | 124 (47.9) | 120 (47.6) | |
| 3+ times/week | 10 (3.9) | 23 (9.1) | |
| Pregnancy-related complications | 31 (12.1) | 23 (9.2) | 0.36 |
| Missing | 0 (0) | 1 (0.4) | |
| Pre-pregnancy body mass index (kg/m2)b | 21.3 ± 3.2 | 21.17 ± 3.30 | 0.41 |
| Missing | 0 (0) | 1 (0.4) | |
| Child characteristics | |||
| Sex | 1.00 | ||
| Boy | 125 (48.3) | 121 (48.0) | |
| Girl | 134 (51.7) | 131 (52.0) | |
| First-born | 126 (48.8) | 116 (46.0) | 0.84 |
| Gestational age (days)b | 275.6 ± 9.6 | 273.3 ± 12.0 | 0.14 |
| Birth weight (g)b | 3084.5 ± 374.8 | 2965.1 ± 456.9 | 0.01 |
| Length (cm)b | 48.1 ± 1.8 | 47.6 ± 2.5 | 0.05 |
| Head circumference (cm)b | 33.3 ± 1.3 | 33.1 ± 1.5 | 0.23 |
| BSID-II mental index score: | 90.7 ± 5.9 | 86.2 ± 9.0 | 0.03 |
| MDIb | |||
| Missing | 0 (0) | 240 (95.2) | |
| BSID-II psychomotor index score: PDIb | 90.8 ± 10.8 | 86.5 ± 12.3 | 0.09 |
| Missing | 0 (0) | 240 (95.2) |
BSID-II: Bayley Scales of Infant Development second edition.
a
Comparison of continuous data between those included and excluded was performed using Mann–Whitney U test. Categorical variables were compared using χ2 test.
b
Mean±SD.