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Table 1 Basic Characteristics of the participants (n = 8776)

From: Correlation between exposure to fine particulate matter and hypertensive disorders of pregnancy in Shanghai, China

Characteristics Total (n = 8776) No HDP (n = 8336) HDP (n = 440) P value
Gestational age at enrollment (days) 104.0 ± 8.7 104.0 ± 8.6 104.3 ± 8.9 0.46
Maternal age at enrollment (year) 30.2 ± 3.6 30.2 ± 3.6 30.4 ± 3.7 0.14
Maternal height (centimeters) 161.7 ± 4.8 161.7 ± 4.8 161.7 ± 5.0 0.85
Maternal weight before pregnancy (kg) 54.8 ± 7.8 54.6 ± 7.5 59.8 ± 10.9 < 0.01
Pre - conception BMI (kg m− 2)
 Underweight (< 18.5) 1408 (16.0) 1372 (16.5) 36 (8.2)  
 Normal (18.5–23) 5706 (65.0) 5486 (73.6) 220 (50.0)  
 Overweight (23–27.5) 1436 (16.4) 1298 (15.6) 138 (31.4)  
 Obesity (≥27.5) 226 (2.6) 180 (2.2) 46 (10.5) < 0.01
Season of conception
 Spring 3136 (35.7) 2951 (35.4) 185 (42.1)  
 Summer 1778 (20.3) 1695 (20.3) 83 (18.9)  
 Autumn 1541 (17.6) 1492 (17.9) 49 (11.1)  
 Winter 2321 (26.5) 2198 (26.4) 123 (27.9) < 0.01
Parity
 Nulliparous 7117 (81.1) 6735 (80.8) 382 (86.8)  
 Multiparous 1659 (18.9) 1601 (19.2) 58 (13.2) < 0.01
Sex of foetus
 Male 4510 (51.4) 4284 (51.4) 226 (51.4)  
 Female 4266 (48.6) 4085 (48.6) 214 (48.6) 0.99
Parental history of chronic diseases
 No 6027 (68.7) 5777 (69.3) 250 (56.8)  
 Yes 2749 (31.3) 2559 (30.7) 190 (43.2) < 0.01
Prenatal care insurance type
 Government-sponsored 6900 (78.6) 6535 (78.4) 365 (83.0)  
 Self-pay 1876 (21.4) 1801 (21.6) 75 (17.0) 0.02