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Table 1 Maternal and Perinatal Baseline Characteristics

From: Association of Ambient air Pollution with risk of preeclampsia during pregnancy: a retrospective cohort study

  PE group
(N = 2988)
non-PE group
(N = 113,054)
χ2 P
Gravidity    1.437 0.231
 1 1089 (36.4) 40,002 (35.4)   
  ≥ 2 1899 (63.6) 73,052 (64.6)
Parity 40.137 < 0.001
 0 1413 (47.3) 49,479 (43.8)   
 1 1355 (45.3) 57,234 (50.6)
  ≥ 2 220 (7.4) 6341 (5.6)
Age (years) 176.188 < 0.001
  < 20 47 (1.6) 1304 (1.2)   
 20–24 472 (15.8) 18,094 (16.0)
 25–29 1201 (40.2) 53,034 (46.9)
 30–34 753 (25.2) 28,463 (25.2)
 35–39 406 (13.6) 10,451 (9.2)
  ≥ 40 109 (3.6) 1708 (1.5)
Education level 84.782 < 0.001
 College and above 956 (32.0) 41,755 (36.9)   
 Middle school 1921 (64.3) 69,307 (61.3)
 Primary school and below 111 (3.7) 1992 (1.8)
Marital status 0.272 0.602
 Married 2974 (99.5) 112,594 (99.6)   
 Single or divorced 14 (0.5) 460 (0.4)
Season of conception 0.134 0.714
 Warm (May to October) 1396 (46.7) 53,202 (47.1)   
 Cold (November to April) 1592 (53.3) 59,852 (52.9)
Season of delivery 3.668 0.160
 Warm (May to October) 1304 (43.6) 48,700 (43.1)   
 Cold (November to April) 1361 (45.5) 53,111 (47.0)
Gestational age (weeks)    5201.901 < 0.001
  ≥ 37 1834 (61.4) 106,660 (94.3)   
  < 37 1154 (38.6) 6394 (5.7)   
  1. Total 116,042 parturients were included. The categorical data were presented as numbers (frequencies, %), Chi-square test was used for categorical data. PE preeclampsia