Table 2.
Baseline characteristics of participants in the China Birth Cohort study
| Characteristics | No. of samples (Mean, 95%CI/median) | Percentage (Standard deviation/IQR) |
|---|---|---|
| Maternal age at pregnancy, years | ||
| Mean age, 95%CI | 30.08, 30.06–30.11 | (4.27) |
| Median age | 30.00 | (27.00–33.00) |
| ≤ 25 | 15354 | 12.75 |
| 26–30 | 53 717 | 44.62 |
| 31–35 | 37761 | 31.37 |
| ≥ 36 | 13545 | 11.25 |
| Paternal age, years | ||
| Mean age (SD) | 31.45, 31.42–31.48 | (4.93) |
| Median age | 31.00 | (28.00–34.00) |
| ≤ 25 | 9888 | 8.21 |
| 26–30 | 46 744 | 38.83 |
| 31–35 | 41455 | 34.44 |
| ≥ 36 | 22290 | 18.52 |
| Maternal ethnicity | ||
| Han | 112712 | 93.63 |
| Others | 7665 | 6.37 |
| Paternal ethnicity | ||
| Han | 113988 | 94.69 |
| Others | 6389 | 5.31 |
| Maternal education | ||
| < College | 27923 | 23.20 |
| Undergraduate/College | 79942 | 66.41 |
| > Postgraduate or higher | 12512 | 10.39 |
| Paternal education | ||
| < College | 30696 | 25.50 |
| Undergraduate/College | 77184 | 64.12 |
| > Postgraduate or higher | 12497 | 10.38 |
| Maternal occupation | ||
| Unemployed | 29293 | 24.33 |
| Office worker | 9820 | 8.16 |
| Doctor or medical service personnel | 4713 | 3.92 |
| Banking or commerce or service staff | 5970 | 4.96 |
| Company staff | 44145 | 36.67 |
| Manufactory worker or farmer | 1652 | 1.37 |
| Teacher or researcher or technician | 11360 | 9.44 |
| Military or police | 281 | 0.23 |
| Others | 13143 | 10.92 |
| Maternal annually income, Yuan* | ||
| < 50 000 | 41195 | 34.22 |
| 50 000–100 000 | 47277 | 39.27 |
| 100 000–200 000 | 23796 | 19.77 |
| 200 000–400 000 | 6328 | 5.26 |
| 400 000–600 000 | 1192 | 0.99 |
| > 600 000 | 589 | 0.49 |
| Family annually income, Yuan* | ||
| < 50 000 | 15138 | 12.58 |
| 50 000–100 000 | 34289 | 28.48 |
| 100 000–200 000 | 39346 | 32.69 |
| 200 000–400 000 | 21067 | 17.50 |
| 400 000–600 000 | 7040 | 5.85 |
| > 600 000 | 3497 | 2.91 |
| Maternal smoking | 225 | 0.19 |
| Paternal smoking | 40665 | 33.78 |
| Maternal alcohol drinking | 3950 | 3.28 |
| Paternal alcohol drinking | 38454 | 31.94 |
| PIH | ||
| Yes | 384 | 0.32 |
| No | 119993 | 99.68 |
| DM | ||
| Yes | 316 | 0.26 |
| No | 120061 | 99.74 |
| Maternal biological families with birth defects | 2038 | 1.69 |
|
Paternal biological families with birth defects Age of menarche, years |
1633 | 1.36 |
| Mean age | 13.20, 13.19–13.21 | (1.27) |
| Median age | 13.00 | (12.00–14.00) |
| < 12 years | 3721 | 3.09 |
| 12–14 years | 99492 | 82.65 |
| > 14 years | 17164 | 14.26 |
| Pre-pregnancy BMI, kg/m2 | ||
| Mean BMI | 22.06, 22.04–22.08 | (4.23) |
| Median BMI | 21.26 | (19.53–23.59) |
| < 18.5 | 16132 | 13.40 |
| 18.5–25 | 85662 | 71.16 |
| 25–30 | 14120 | 11.73 |
| ≥ 30 | 4463 | 3.71 |
| Paternal BMI, kg/m2 | ||
| Mean BMI | 24.96, 24.93–24.99 | (4.95) |
| Median BMI | 24.24 | (22.13–26.73) |
| < 18.5 | 3212 | 2.67 |
| 18.5–25 | 67430 | 56.02 |
| 25–30 | 39628 | 32.92 |
| ≥ 30 | 10107 | 8.40 |
| Fertilization way | ||
| Natural pregnancy | 114679 | 95.27 |
| Artificial insemination | 637 | 0.53 |
| IVF | 5061 | 4.20 |
| Nulliparous | 58818 | 48.86 |
*1 dollar = 7 yuan. PIH: pregnancy induced hypertension. DM: diabetes mellitus. IQR: interquartile range