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Table 1 Basic characteristics of low birth weight cases and controls [n (%)]

From: Maternal urinary manganese and risk of low birth weight: a case–control study

Characteristics Cases (n = 204) Controls (n = 612)
Infant sex   
 Male 101 (49.5) 303 (49.5)
 Female 103 (50.5) 309 (50.5)
Maternal age   
  < 25 years 48 (23.5) 146 (23.8)
 25–29 years 81 (39.7) 242 (39.5)
  ≥ 30 years 75 (36.7) 224 (36.6)
Education   
  ≤ 9 years 89 (43.6) 167 (27.3)
 9–12 years 38 (18.6) 120 (19.6)
  > 12 years 77 (37.8) 322 (52.6)
 Missing 0 (0.0) 3 (0.5)
Household income   
  < 50,000 yuan per year 116 (56.9) 275 (44.9)
  ≥ 50,000 yuan per year 61 (29.9) 279 (45.6)
 Missing 27 (13.2) 58 (9.5)
Parity   
 Primiparous 159 (77.9) 501 (81.9)
 Multiparous 45 (22.1) 111 (18.1)
Gestational hypertension   
 Yes 20 (9.8) 12 (2.0)
 No 183 (89.7) 598 (97.7)
 Missing 1 (0.5) 2 (0.3)
Gestational diabetes   
 Yes 7 (3.4) 27 (4.4)
 No 197 (96.6) 585 (95.6)
Pre-pregnancy BMI   
  < 18.5 kg/m2 60 (29.4) 125 (20.4)
 18.5–23.9 kg/m2 108 (52.9) 385 (62.9)
  ≥ 24 kg/m2 26 (12.8) 85 (13.9)
 Missing 10 (4.9) 17 (2.8)
Multivitamin supplement during pregnancy  
 Yes 137 (67.2) 409 (66.8)
 No 59 (28.9) 190 (31.1)
 Missing 8 (3.9) 13 (2.1)
Smoking during pregnancy   
 No 198 (97.1) 608 (99.4)
 Yes 1 (0.5) 0 (0.0)
 Missing 5 (2.4) 4 (0.6)
Passive smoking during pregnancy  
 Yes 47 (23.0) 129 (21.1)
 No 149 (73.0) 464 (75.8)
 Missing 8 (3.9) 19 (3.1)
Alcohol use during pregnancy   
 Yes 2 (1.0) 1 (3.3)
 No 196 (96.1) 594 (97.1)
 Missing 6 (2.9) 17 (2.8)