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Table 1 Characteristics of participants by trimesters

From: Prevalence of anemia and iron deficiency anemia in Chinese pregnant women (IRON WOMEN): a national cross-sectional survey

Characteristics Total (n,%) First trimester (n,%) Second trimester
(n,%)
Third trimester
(n,%)
P value
Number 12,403 (100.0) 1018 (8.21) 3487 (28.11) 7898 (63.68) ____
Regions
 Southwest 2105 (16.97) 214 (21.02) 693 (19.87) 1198 (15.17)  
 East 2008 (16.19) 123 (12.08) 484 (13.88) 1401 (17.74)  
 Central-south 2044 (16.48) 181 (17.78) 601 (17.24) 1262 (15.98)  
 Northeast 2179 (17.57) 38 (3.73) 469 (13.45) 1672 (21.17)  
 Northwest 2051 (16.54) 231 (22.69) 711 (20.39) 1109 (14.04)  
 North 2016 (16.25) 231 (22.69) 529 (15.17) 1256 (15.90) < 0.0011
Maternal age
  < 35 years 10,595 (85.42) 893 (87.72) 2974 (85.29) 6728 (85.19)  
  ≥ 35 years 1808 (14.58) 125 (12.28) 513 (14.71) 1170 (14.81) 0.091
Ethnicity
 Han 11,542 (93.06) 959 (94.20) 3257 (93.40) 7326 (92.76)  
 Others 861 (6.94) 59 (5.80) 230 (6.60) 572 (7.24) 0.1481
Education level
  ≥ 17 years 1376 (11.09) 120 (11.79) 372 (10.67) 884 (11.19)  
 13–16 years 8403 (67.75) 699 (68.66) 2306 (66.13) 5398 (68.35)  
 10–12 years 1698 (13.69) 140 (13.75) 522 (14.97) 1036 (13.12)  
  ≤ 9 years 926 (7.47) 59 (5.80) 287 (8.23) 580 (7.34) 0.021
Local residents
 No 1394 (11.24) 120 (11.79) 463 (13.28) 811 (10.27)  
 Yes 11,009 (88.76) 898 (88.21) 3024 (86.72) 7087 (89.73) < 0.0011
Registered residential place
 Urban 6367 (51.33) 516 (50.69) 1806 (51.79) 4045 (51.22)  
 Rural 6036 (48.67) 502 (49.31) 1681 (48.21) 3853 (48.78) 0.7761
Annual family income (thousand yuan)
  < 30 1167 (9.41) 72 (7.07) 320 (9.18) 775 (9.81)  
 30–79.9 3427 (27.63) 263 (25.83) 994 (28.51) 2170 (27.48)  
 80–119.9 3351 (27.02) 301 (29.57) 1010 (28.96) 2040 (25.83)  
 120–199.9 2549 (20.55) 228 (22.40) 686 (19.67) 1635 (20.70)  
  ≥ 200 1909 (15.39) 154 (15.13) 477 (13.68) 1278 (16.18) < 0.0011
Multiple gestations
 No 12,121 (97.84) 996 (96.70) 3372 (98.16) 7753 (97.73)  
 Yes 282 (2.16) 22 (3.30) 115 (1.84) 145 (2.27) < 0.0011
Parity
 Nulliparity 8268 (66.66) 713 (70.04) 2290 (65.67) 5265 (66.66)  
 Multiparity 4135 (33.34) 305 (29.96) 1197 (34.33) 2633 (33.34) 0.0341
Use of ART
 No 11,921 (96.11) 969 (95.19) 3296 (94.52) 7656 (96.94)  
 Yes 482 (3.89) 49 (4.81) 191 (5.48) 242 (3.06) < 0.0011
NVP
 No 2957 (23.84) 167 (16.40) 715 (20.50) 2075 (26.27)  
 Slight 7496 (60.44) 671 (65.91) 2196 (62.98) 4629 (58.61)  
 Severe 1950 (15.72) 180 (17.68) 576 (16.52) 1194 (15.12) < 0.0011
Pre-pregnancy BMI
 Underweight 2147 (17.31) 178 (17.49) 625 (17.92) 1344 (17.02)  
 Normal weight 8925 (71.96) 738 (72.50) 2467 (70.75) 5720 (72.42)  
 Overweight and obese 1331 (10.73) 102 (10.02) 395 (11.33) 834 (10.56) 0.4051
Active or passive smoking
 No 7710 (57.37) 584 (62.46) 2178 (62.65) 4948 (62.16)  
 Yes 4693 (42.63) 434 (37.54) 1309 (37.35) 2950 (37.84) 0.0041
Meat intake (kg/week)a 0.30 (0.15–0.45) 0.15 (0.10–0.35) 0.25 (0.10–0.4) 0.30 (0.15–0.50) < 0.0012
Intake of folic acid
 No 2077 (16.75) 181 (17.78) 530 (15.20) 1366 (17.30)  
 Yes 10,326 (83.25) 837 (82.22) 2957 (84.80) 6532 (82.70) 0.0141
Intake of multivitamins
 No 4305 (34.71) 517 (50.79) 1322 (37.91) 2466 (31.22)  
 Yes 8098 (65.29) 501 (49.21) 2165 (62.09) 5432 (68.78) < 0.0011
Intake of calcium
 No 4367 (35.21) 887 (87.13) 1664 (47.72) 1816 (22.99)  
 Yes 8036 (64.79) 131 (12.87) 1823 (52.28) 6082 (77.01) < 0.0011
Hematological diseases
 No 11,782 (94.99) 987 (96.95) 3365 (96.50) 7430 (94.07)  
 Yes 621 (5.01) 31 (3.05) 122 (3.50) 468 (5.93) < 0.0011
HBV infection
 No 12,097 (97.53) 999 (98.13) 3405 (97.65) 7693 (97.40)  
 Yes 306 (2.47) 19 (1.87) 82 (2.35) 205 (2.60) 0.3231
Hypertension
 No 12,363 (99.68) 1012 (99.41) 3473 (99.60) 7878 (99.75)  
 Yes 40 (0.32) 6 (0.59) 14 (0.40) 20 (0.25) 0.1281
Gynecological diseases
 No 11,719 (94.49) 933 (91.65) 3288 (94.29) 7498 (94.94)  
 Yes 684 (5.51) 85 (8.35) 199 (5.71) 400 (5.06) < 0.0011
Diabetes
 No 12,346 (99.51) 1013 (99.51) 3470 (99.51) 7863 (99.56)  
 Yes 57 (0.49) 5 (0.49) 17 (0.49) 35 (0.44) 0.9381
Thyroid diseases
 No 11,734 (94.61) 977 (95.97) 3295 (94.49) 7462 (94.48)  
 Yes 669 (5.39) 41 (4.03) 192 (5.51) 436 (5.52) 0.1311
Autoimmune diseases
 No 12,356 (99.62) 1010 (99.21) 3461 (99.25) 7885 (99.84)  
 Yes 47 (0.38) 8 (0.79) 26 (0.75) 13 (0.16) < 0.0011
Digestive system diseases
 No 11,881 (95.79) 949 (93.22) 3331 (95.53) 7601 (96.24)  
 Yes 522 (4.21) 69 (6.78) 156 (4.47) 297 (3.76) < 0.0011
  1. 1From Pearson’s chi-square test
  2. 2From Kruskal-Wallis rank test
  3. aMedian (lower quartile-upper quartile)
  4. ART assisted reproductive technology; NVP nausea or vomiting during pregnancy; HBV hepatitis B viral; BMI Body Mass Index