Table 1. Baseline characteristics of 5,169,812 reproductive-aged women in China, 2013–2017.
| Maternal characteristic | Total (n=5,169,812) | ALT level (U/L) | P value* | ||
| <20 (n=3,223,504) | 20–40 (n=1,681,607) | >40 (n=264,701) | |||
| Abbreviation: ALT=alanine aminotransferase; IQR=interquartile range; SD=standard deviation; LMP=last menstrual period; BMI=body mass index; HBsAg=hepatitis B surface antigen. * Multiple comparison with Bonferroni-adjusted P<0.05 compared with the ALT 20–40 U/L group (<20 U/L group vs. 20–40 U/L group; >40 U/L group vs. 20–40 U/L group). † The Kruskal-Wallis H test was used to examine the differences of baseline characteristics among ALT groups; otherwise, the χ2 test was used. | |||||
| Age at LMP (years), mean (SD) | 26.52 (4.21) | 26.52 (4.16) | 26.52 (4.30) | 26.46 (4.27) | <0.001† |
| Age at LMP (years), n (%) | <0.001† | ||||
| 20–24 | 1,811,519 (35.04) | 1,112,313 (34.51) | 601,897 (35.79) | 97,309 (36.76) | |
| 25–29 | 2,327,309 (45.02) | 1,477,004 (45.82) | 736,831 (43.82) | 113,474 (42.87) | |
| 30–34 | 741,964 (14.35) | 459,234 (14.25) | 243,827 (14.50) | 38,903 (14.70) | |
| 35–39 | 241,702 (4.68) | 147,047 (4.56) | 81,958 (4.87) | 12,697 (4.80) | |
| ≥40 | 47,318 (0.92) | 27,906 (0.87) | 17,094 (1.02) | 2,318 (0.88) | |
| Preconception BMI (kg/m2), n (%) | <0.001† | ||||
| <18.5 | 698,452 (13.51) | 481,090 (14.92) | 189,707 (11.28) | 27,655 (10.45) | |
| 18.5–23.9 | 3,665,734 (70.91) | 2,295,998 (71.23) | 1,196,830 (71.17) | 172,906 (65.32) | |
| 24.0–27.9 | 635,294 (12.29) | 356,654 (11.06) | 232,028 (13.80) | 46,612 (17.61) | |
| ≥28 | 145,745 (2.82) | 71,746 (2.23) | 57,561 (3.42) | 16,438 (6.21) | |
| Missing | 24,587 (0.48) | 18,016 (0.56) | 5,481 (0.33) | 1,090 (0.41) | |
| Education, n (%) | <0.001 | ||||
| Junior high school and below | 3,135,739 (60.65) | 1,892,092 (58.70) | 1,079,663 (64.20) | 163,984 (61.95) | |
| Senior high school or above | 1,879,334 (36.35) | 1,226,039 (38.03) | 561,238 (33.38) | 92,057 (34.78) | |
| Missing | 154,739 (2.99) | 105,373 (3.27) | 40,706 (2.42) | 8,660 (3.27) | |
| Nationality, n (%) | <0.001 | ||||
| Han | 4,754,322 (91.96) | 2,973,137 (92.23) | 1,541,688 (91.68) | 239,497 (90.48) | |
| Other | 354,381 (6.85) | 208,609 (6.47) | 124,208 (7.39) | 21,564 (8.15) | |
| Missing | 61,109 (1.18) | 41,758 (1.30) | 15,711 (0.93) | 3,640 (1.38) | |
| Occupation, n (%) | <0.001 | ||||
| Farmer | 3,670,941 (71.01) | 2,215,353 (68.72) | 1,268,826 (75.45) | 186,762 (70.56) | |
| Non-farmer | 1,329,778 (25.72) | 893,104 (27.71) | 368,175 (21.89) | 68,499 (25.88) | |
| Missing | 169,093 (3.27) | 115,047 (3.57) | 44,606 (2.65) | 9,440 (3.57) | |
| Residence, n (%) | <0.001 | ||||
| Rural | 4,719,410 (91.29) | 2,915,213 (90.44) | 1,561,686 (92.87) | 242,511 (91.62) | |
| Urban | 449,991 (8.70) | 307,948 (9.55) | 119,867 (7.13) | 22,176 (8.38) | |
| Missing | 411 (0.01) | 343 (0.01) | 54 (0.00) | 14 (0.01) | |
| Region, n (%) | <0.001 | ||||
| Eastern | 1,800,946 (34.84) | 1,539,760 (47.77) | 889,719 (52.91) | 89,548 (33.83) | |
| Central | 2,552,013 (49.36) | 1,236,843 (38.37) | 474,555 (28.22) | 122,534 (46.29) | |
| Western | 816,853 (15.80) | 446,901 (13.86) | 317,333 (18.87) | 52,619 (19.88) | |
| Parity, n (%) | <0.001 | ||||
| Primipara | 3,158,062 (61.09) | 1,960,188 (60.81) | 1,030,173 (61.26) | 167,701 (63.35) | |
| Multipara | 2,011,750 (38.91) | 1,263,316 (39.19) | 651,434 (38.74) | 97,000 (36.65) | |
| Hypertension, n (%) | <0.001 | ||||
| No | 5,055,184 (97.78) | 3,154,849 (97.87) | 1,644,195 (97.78) | 256,140 (96.77) | |
| Yes | 81,071 (1.57) | 47,032 (1.46) | 27,382 (1.63) | 6,657 (2.51) | |
| Missing | 33,557 (0.65) | 21,623 (0.67) | 10,030 (0.60) | 1,904 (0.72) | |
| Hyperglycemia, n (%) | <0.001 | ||||
| No | 4,937,590 (95.51) | 3,079,691 (95.54) | 1,612,949 (95.92) | 244,950 (92.54) | |
| Yes | 201,358 (3.89) | 123,428 (3.83) | 59,698 (3.55) | 18,232 (6.89) | |
| Missing | 30,864 (0.60) | 20,385 (0.63) | 8,960 (0.53) | 1,519 (0.57) | |
| Smoking, n (%) | <0.001 | ||||
| No | 5,132,139 (99.27) | 3,198,243 (99.22) | 1,671,189 (99.38) | 262,707 (99.25) | |
| Yes | 10,608 (0.21) | 6,761 (0.21) | 3,156 (0.19) | 691 (0.26) | |
| Missing | 27,065 (0.52) | 18,500 (0.57) | 7,262 (0.43) | 1,303 (0.49) | |
| Drinking, n (%) | <0.001 | ||||
| No | 4,997,403 (96.67) | 3,104,545 (96.31) | 1,636,845 (97.34) | 256,013 (96.72) | |
| Yes | 140,600 (2.72) | 97,448 (3.02) | 36,014 (2.14) | 7,138 (2.70) | |
| Missing | 31,809 (0.62) | 21,511 (0.67) | 8,748 (0.52) | 1,550 (0.59) | |
| Periconception folic acid intake, n (%) | <0.001 | ||||
| No | 1,059,359 (20.49) | 650,583 (20.18) | 354,576 (21.09) | 54,200 (20.48) | |
| Yes | 4,055,168 (78.44) | 2,536,091 (78.67) | 1,311,328 (77.98) | 207,749 (78.48) | |
| Missing | 55,285 (1.07) | 36,830 (1.14) | 15,703 (0.93) | 2,752 (1.04) | |
| Preconception harmful exposure, n (%) | <0.001 | ||||
| No | 4,555,857 (88.12) | 2,815,462 (87.34) | 1,508,161 (89.69) | 232,234 (87.73) | |
| Yes | 586,854 (11.35) | 389,622 (12.09) | 166,073 (9.88) | 31,159 (11.77) | |
| Missing | 27,101 (0.52) | 18,420 (0.57) | 7,373 (0.44) | 1,308 (0.49) | |
| History of adverse pregnancy outcomes, n (%) | <0.001 | ||||
| No | 4,337,030 (83.89) | 2,684,307 (83.27) | 1,436,552 (85.43) | 216,171 (81.67) | |
| Yes | 832,782 (16.11) | 539,197 (16.73) | 245,055 (14.57) | 48,530 (18.33) | |
| Serum HBsAg status, n (%) | <0.001 | ||||
| Negative | 4,920,895 (95.19) | 3,109,439 (96.46) | 1,579,261 (93.91) | 232,195 (87.72) | |
| Positive | 244,832 (4.74) | 111,470 (3.46) | 101,070 (6.01) | 32,292 (12.20) | |
| Missing | 4,085 (0.08) | 2,595 (0.08) | 1,276 (0.08) | 214 (0.08) | |