Table 1.
Characteristics of the study population
| Baseline characteristics | Primipara | Multipara | P |
|---|---|---|---|
| Maternal age, yeara | 25.19 (3.69) | 29.60 (4.71) | <0.001 |
| Gestational age, weeka | 39.65 (1.29) | 39.64 (1.24) | 0.549 |
| Sex of infants, n (%) | |||
| Boy | 8789 (52.70) | 5959 (55.82) | <0.001 |
| Girl | 7887 (47.30) | 4716 (44.18) | |
| Season of birth, n (%) | |||
| Spring | 4237 (25.41) | 2803 (26.26) | <0.001 |
| Summer | 3878 (23.25) | 2669 (25.00) | |
| Fall | 4166 (24.98) | 2595 (24.31) | |
| Winter | 4395 (26.36) | 2608 (24.43) | |
| Region, n (%) | |||
| Central Shaanxi | 9513 (57.05) | 5367 (50.28) | <0.001 |
| Northern Shaanxi | 3750 (22.49) | 3105 (29.09) | |
| Southern Shaanxi | 3413 (20.46) | 2203 (20.63) | |
| Mother’s education, n (%) | |||
| Primary school or less | 917 (5.51) | 2095 (19.67) | <0.001 |
| Junior high school | 6992 (42.03) | 6524 (61.25) | |
| Senior high school | 4044 (24.31) | 1559 (14.64) | |
| College and above | 4683 (28.15) | 473 (4.44) | |
| Residence, n (%) | |||
| Urban area | 4643 (27.95) | 1135 (10.68) | <0.001 |
| Rural area | 11,968 (72.05) | 9492 (89.32) | |
| Mother’s occupation, n (%) | |||
| Peasant/Housework | 8932 (53.56) | 8275 (77.52) | <0.001 |
| Other | 7744 (46.44) | 2400 (22.48) | |
| Household Wealth Index, n (%) | |||
| Poorest | 3302 (22.10) | 2903 (29.13) | <0.001 |
| Middle | 7765 (51.96) | 5605 (56.25) | |
| Richest | 3876 (25.94) | 1456 (14.62) | |
aReported as mean and SD (standard deviation)