Table 1.
Serum 25 hydroxyvitamin D concentration of pregnant women in CNHS 2010–2012 and CNHS 2015–2017 (P50 (P25~P75), ng/mL).
| Characteristics | CNHS 2010–2012 | CNHS 2015–2017 | p | ||
|---|---|---|---|---|---|
| N (%) | Concentration | N (%) | Concentration | ||
| Total | 2006 | 15.48 (11.89–20.09) | 8200 | 13.02 (10.17–17.01) | <0.0001 |
| City type | |||||
| Urban | 1027 (51.20%) | 15.41 (11.79–20.23) | 4909 (59.87%) | 12.94 (10.11–16.95) | <0.0001 |
| Rural | 979 (48.80%) | 15.55 (11.95–19.91) | 3291 (40.13%) | 13.17 (10.26–17.11) | <0.0001 |
| District | |||||
| Eastern | 773 (38.53%) | 16.89 (13.06–22.38) a | 2869 (34.99%) | 14.19 (10.88–18.63) a | <0.0001 |
| Central | 716 (35.69%) | 15.55 (12.11–19.83) b | 2557 (31.18%) | 12.44 (9.99–15.73) b | <0.0001 |
| Western | 517 (25.77%) | 13.74 (9.8–17.73) c | 2774 (33.83%) | 12.65 (9.58–16.45) b | 0.003 |
| Location | |||||
| Southern | 1007 (50.20%) | 17.11 (13.23–21.53) a | 3856 (47.02%) | 15.05 (11.65–18.98) a | <0.0001 |
| Northern | 999 (49.80%) | 14.03 (10.91–18.34) b | 4344 (52.98%) | 11.37 (9.11–14.18) b | <0.0001 |
| Age group | |||||
| 18–24.9 y | 785 (39.13%) | 14.92 (11.46–19.13) b | 2055 (25.06%) | 13.02 (10.13–16.95) | <0.0001 |
| 25–29.9 y | 797 (39.73%) | 15.85 (12.36–20.29) a | 3889 (47.43%) | 12.92 (10.17–16.85) | <0.0001 |
| 30–34.9 y | 313 (15.60%) | 16.01 (12.16–21.53) a | 1610 (19.63%) | 13.26 (10.19–17.36) | <0.0001 |
| 35 y+ | 111 (5.53%) | 15.77 (12.06–20.3) ab | 646 (7.88%) | 13.24 (10.44–17.19) | <0.001 |
| Latitude | |||||
| tropical | 130 (6.48%) | 21.31 (16.37–24.98) a | 577 (7.04%) | 18.63 (14.54–23.38) a | <0.0001 |
| subtropical | 786 (39.18%) | 16.65 (12.84–20.67) b | 3203 (39.06%) | 14.98 (11.99–18.63) b | <0.0001 |
| warm temperate | 776 (38.68%) | 13.4 (10.68–17.59) c | 3202 (39.05%) | 11.24 (9.00–14.18) c | <0.0001 |
| medium temperate | 314 (15.65%) | 16.19 (12.6–21.27) b | 1218 (14.85%) | 11.83 (9.54–14.66) c | <0.0001 |
| Nationality | |||||
| Han | 1813 (90.38%) | 15.62 (12.06–20.29) a | 7221 (88.06%) | 13.02 (10.23–17.09) a | <0.0001 |
| Ethnic minorities | 193 (9.62%) | 14.24 (10.29–18.45) b | 979 (11.94%) | 12.9 (9.62–16.65) b | <0.0001 |
| Gestational age | |||||
| First trimester | 462 (23.03%) | 15.92 (12.6–20.53) | 2352 (28.68%) | 12.95 (10.22–16.74) | <0.0001 |
| Second trimester | 909 (45.31%) | 15.59 (11.75–20.27) | 3424 (41.76%) | 13.09 (10.23–17.15) | <0.0001 |
| Third trimester | 635 (31.66%) | 14.79 (11.8–19.12) | 2424 (29.56%) | 13.02 (9.98–17.11) | <0.0001 |
| Pregnant frequency | |||||
| 1 | 1278 (63.71%) | 15.15 (11.73–19.42) b | 3739 (45.60%) | 12.83 (9.97–16.69) b | <0.0001 |
| 2 | 567 (28.27%) | 15.79 (12.29–21.39) a | 3131 (38.18%) | 13.16 (10.31–17.18) a | <0.0001 |
| 3+ | 161 (8.03%) | 16.79 (12.56–20.67) a | 1330 (16.22%) | 13.42 (10.49–17.55) a | <0.0001 |
| BMI before pregnancy | |||||
| Thin | 98 (4.89%) | 18.8 (13.73–24.23) a | 305 (3.72%) | 14.18 (10.88–18.44) a | <0.0001 |
| Normal | 939 (46.81%) | 15.69 (11.82–20.32) b | 3830 (46.71%) | 13.29 (10.42–17.33) a | <0.0001 |
| Overweight | 707 (35.24%) | 14.98 (11.79–19.04) b | 2692 (32.83%) | 12.88 (9.97–16.68) b | <0.0001 |
| Obesity | 262 (13.06%) | 15.62 (11.9–19.14) b | 1373 (16.74%) | 12.68 (9.71–16.43) b | <0.0001 |
| Season | |||||
| Spring | 55 (2.74%) | 9.77 (8.46–11.22) c | 896 (10.93%) | 12.27 (9.45–16.41) c | <0.0001 |
| Summer | 50 (2.49%) | 17.51 (13.29–23.08) a | 30 (0.37%) | 17.52 (13.96–21.16) a | 0.968 |
| Autumn | 963 (48.01%) | 16.76 (12.74–21.55) a | 1870 (22.80%) | 14.76 (11.67–18.42) b | <0.0001 |
| Winter | 938 (46.76%) | 14.68 (11.43–18.95) b | 5404 (65.90%) | 12.57 (9.84–16.42) c | <0.0001 |
| Vitamin D supplement intake | |||||
| No | 1793 (89.38%) | 15.47 (11.85–19.97) | 7833 (95.52%) | 12.96 (10.14–16.91) b | <0.0001 |
| Yes | 180 (8.97%) | 15.55 (12.73–21.29) | 367 (4.48%) | 14.89 (11.2–18.37) a | 0.003 |
| unknown | 33 (1.65%) | 14.66 (10.56–19.52) | / | / | |
| Education | |||||
| Primary | 145 (7.23%) | 15.71 (11.32–20.77) | 532 (6.49%) | 12.63 (9.72–16.33) b | <0.0001 |
| Medium | 1221 (60.87%) | 15.55 (12.08–19.98) | 4243 (51.74%) | 13.3 (10.31–17.24) a | <0.0001 |
| Advanced | 640 (31.90%) | 15.35 (11.65–19.85) | 3425 (41.77%) | 12.8 (10.07–16.78) b | <0.0001 |
| Marital status | |||||
| Unmarried | 38 (1.89%) | 13.46 (11.79–17.74) | 67 (0.82%) | 14.57 (11.63–18.29) | 0.492 |
| Married | 1968 (98.11%) | 15.51 (11.9–20.16) | 8133 (99.18%) | 13.01 (10.16–16.98) | <0.0001 |
| Annual family income per capita | |||||
| Low | 630 (31.41%) | 15.3 (11.83–19.37) | 1734 (21.15%) | 12.39 (9.56–15.94) | <0.0001 |
| Mid | 744 (37.09%) | 15.25 (12.04–19.96) | 1677 (20.45%) | 12.64 (9.82–16.56) | <0.0001 |
| High | 462 (23.03%) | 16.46 (11.89–21.00) | 1890 (23.05%) | 13.64 (10.63–17.73) | <0.0001 |
| NR * | 170 (8.47%) | 15.73 (11.86–20.42) | 2899 (35.35%) | 13.35 (10.41–17.49) | <0.0001 |
a,b,c refers to statistical difference in groups, p < 0.05; * NR—not reported.