Table 1 Characteristics of participants by trimesters
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 |