Table 1.
Basic characteristics of study participants.
| Characteristic | Total | Year 2017 | Year 2018 | Year 2019 |
|---|---|---|---|---|
| n = 119,286 | n = 100,521 | n = 8,829 | n = 9,936 | |
| Age (year) | 28.3 ± 4.4 | 28.3 ± 4.5 | 28 ± 4.5 | 28.2 ± 4.2 |
| Age group, n(%) | ||||
| <35 | 107,627 (90.2%) | 90,345 (89.9%) | 8,076 (91.5%) | 9,206 (92.7%) |
| ≥35 | 11,659 (9.8%) | 10,176 (10.1%) | 753 (8.5%) | 730 (7.3%) |
| Age category, n(%) | ||||
| <20 | 1,230 (1.0) | 1,000 (1.0) | 139 (1.6) | 91 (0.9) |
| 20– | 76,625 (64.2) | 64,531 (64.2) | 5,744 (65.0) | 6,350 (63.9) |
| 30– | 39,711 (33.3) | 33,477 (33.3) | 2,823 (32) | 3,411 (34.3) |
| 40– | 1,720 (1.5) | 1,513 (1.5) | 123 (1.4) | 84 (0.9) |
| Gestational age, n(%)a | ||||
| 1st trimester | 22,800 (51.6) | 19,101 (50.4) | 1,715 (48.3) | 1,984 (72.3) |
| 2nd trimester | 6,999 (15.8) | 5,675 (15) | 836 (23.6) | 488 (17.8) |
| 3rd trimester | 14,416 (32.6) | 13,145 (34.6) | 999 (28.1) | 272 (9.9) |
| Region, n(%)b | ||||
| Shaanxi | 82,735 (72.9) | 66,237 (69.9) | 7,715 (87.4) | 8,783 (88.4) |
| Ningxia | 5,509 (4.9) | 5,154 (5.4) | 254 (2.9) | 101 (1.0) |
| Qinghai | 10,846 (9.5) | 10,139 (10.7) | 567 (6.4) | 140 (1.4) |
| Shanxi | 14,433 (12.7) | 13,228 (14.0) | 293 (3.3) | 912 (9.2) |
| Season of vitamin test, n(%) | ||||
| Spring | 30,399 (25.5) | 24,984 (24.9) | 2,680 (30.4) | 2,735 (27.5) |
| Summer | 33,944 (28.5) | 29,141 (29.0) | 2,128 (24.1) | 2,675 (26.9) |
| Autumn | 31,403 (26.3) | 26,850 (26.7) | 2,140 (24.2) | 2,413 (24.3) |
| Winter | 23,540 (19.7) | 19,546 (19.4) | 1,881 (21.3) | 2,113 (21.3) |
| Vitamin level | ||||
| Vitamin A (mg/L) | 0.4 (0.33–0.46) |
0.4 (0.33–0.47) |
0.38 (0.32–0.44) |
0.4 (0.34–0.46) |
| Vitamin E (mg/L) | 12.8 (10.5–15.7) |
12.9 (10.6–15.9) |
12.1 (10.2–14.8) |
11.9 (10–14.4) |
| Vitamin D (ng/mL) | 15.5 (10.5–22.9) |
17.8 (11.9–26.7) |
14.4 (9.8–20.9) |
14.4 (9.9–21) |
| Vitamin D2 (ng/mL) | 0.6 (0.4–0.9) |
– | 0.6 (0.4–0.9) |
0.5 (0.4–0.8) |
| Vitamin D3 (ng/mL) | 13.4 (9–20) |
– | 13.3 (8.9–20) |
13.5 (9–20) |
Age was presented as mean ± standard deviation and vitamin levels were presented as median [interquartile range (IQR)].
a
44,215 cases of gestational age information;
b
113,523 cases of region information.