Table 1 Characteristics of participants (n = 17,728)
Variables | Mean or n | SD or %a |
|---|---|---|
Maternal characteristics | ||
 Maternal age (years), n and % | ||
   <  25 | 1283 | 7.2 |
  25–29 | 4493 | 25.3 |
  30–34 | 6572 | 37.1 |
  ≧ 35 | 5380 | 30.3 |
  Number of missing values | 0 | 0 |
 Pre-pregnancy body mass index (kg/m2), mean and SD | 21.6 | 3.4 |
  Number of missing values, n and % | 228 | 1.3 |
 Maternal gestational weight gain (kg), mean and SD | 10.1 | 4.2 |
  Number of missing values, n and % | 4152 | 23.4 |
 Gestational age (week), mean and SD | 39.0 | 1.2 |
  Number of missing values, n and % | 0 | 0 |
 Parity, n and % | ||
  One or more | 9173 | 51.7 |
  Never | 8555 | 48.3 |
  Number of missing values | 0 | 0 |
 Educational qualification, n and % | ||
  High school graduate or less | 3676 | 20.7 |
  College graduate | 4417 | 24.9 |
  University graduate or above | 3313 | 18.7 |
  Number of missing values | 6322 | 35.7 |
 Annual household income (Japanese yen/year), n and % | ||
   <  4,000,000 | 6108 | 34.5 |
  4,000,000–5,999,999 | 5525 | 31.2 |
  ≧ 6,000,000 | 5287 | 29.8 |
  Number of missing values | 808 | 4.6 |
 Cigarette smoking, n and % | ||
  Never | 10,698 | 60.3 |
  Quit before pregnancy | 4075 | 23.0 |
  Quit after noticing pregnancy | 2487 | 14.0 |
  Current | 410 | 2.3 |
  Number of missing values | 58 | 0.3 |
 Alcohol consumption, n and % | ||
  Never | 8016 | 45.2 |
  Former | 6118 | 34.5 |
  Current | 3547 | 20.0 |
  Number of missing values | 47 | 0.3 |
 Folic acid supplement consumption during early pregnancy, n and % | ||
  Yes | 9990 | 56.4 |
  No | 7708 | 43.5 |
  Number of missing values | 30 | 0.2 |
Child characteristics | ||
 Sex, n and % | ||
  Boys | 9159 | 51.7 |
  Girls | 8569 | 48.3 |
  Number of missing values | 0 | 0 |
 Birth weight (g), mean and SD | 3072 | 368 |
  Number of missing values, n and % | 0 | 0 |
 Birth weight SD score, mean and SD | 0.15 | 0.96 |
  Number of missing values, n and % | 0 | 0 |
 Small for gestational age, n and % | ||
  Yes | 1116 | 6.3 |
  No | 16,612 | 93.7 |
  Number of missing values | 0 | 0 |