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Table 1 Characteristics of the women in relation to ELF-MF parameters

From: Prenatal exposure to extremely low frequency magnetic field and its impact on fetal growth

Characteristics N Median (Q1, Q3)(mG)
TWA P50 P75
Total 128 0.63 (0.38,1.09) 0.38 (0.23,0.68) 0.63 (0.38,1.17)
Maternal age at child birth (years)
 <25 14 0.45 (0.28,0.63)* 0.36 (0.18,0.48) 0.50 (0.33,0.68)*
 25–30 79 0.64 (0.38,1.04) 0.38 (0.23,0.63) 0.63 (0.38,1.17)
  > 30 35 0.71 (0.45,1.49) 0.48 (0.23,0.82) 0.82 (0.38,1.52)
Maternal BMI before pregnancy (kg/m2)
 <18.5 28 0.64 (0.41,1.11) 0.41 (0.28,0.70) 0.66 (0.41,1.15)
 18.5–24 93 0.58 (0.37,1.04) 0.38 (0.18,0.63) 0.57 (0.33,1.17)
  > 24 7 1.22 (0.39,1.53) 0.82 (0.23,0.97) 1.13 (0.48,1.52)
Maternal education level
 Middle school and below 7 0.66 (0.58,0.90) 0.38 (0.33,0.48) 0.57 (0.57,0.77)
 High school 15 0.75 (0.35,1.56) 0.43 (0.18,0.77) 0.68 (0.33,1.73)
 College and undergraduate 96 0.64 (0.39,1.10) 0.43 (0.23,0.72) 0.66 (0.38,1.17)
 Postgraduate and above 10 0.33 (0.23,0.80) 0.21 (0.13,0.52) 0.33 (0.23,0.88)
Maternal employment
 Manual labor 84 0.64 (0.38,1.06) 0.43 (0.23,0.70) 0.66 (0.38,1.17)
 Mental labor 30 0.49 (0.37,0.90) 0.36 (0.23,0.52) 0.55 (0.43,0.88)
 Others 14 0.79 (0.57,1.36) 0.56 (0.33,1.17) 0.88 (0.57,1.52)
Average family income / month*person (RMB)
  < 4000 28 0.70 (0.44,1.40) 0.48 (0.28,0.80) 0.70 (0.43,1.68)
 4000~10,000 75 0.58 (0.38,1.07) 0.38 (0.23,0.63) 0.63 (0.38,1.13)
  > 10,000~ 24 0.64 (0.32,1.05) 0.31 (0.18,0.62) 0.67 (0.38,1.33)
Maternal passive smoking
 Yes 56 0.53 (0.37,0.88) 0.36 (0.21,0.68) 0.52 (0.36,1.03)
 No 69 0.67 (0.40,1.10) 0.43 (0.23,0.63) 0.77 (0.43,1.48)
Parity
 1 111 0.63 (0.38,1.10) 0.43 (0.23,0.68) 0.63 (0.38,1.17)
  ≥ 2 17 0.69 (0.25,1.08) 0.33 (0.18,0.63) 0.57 (0.33,1.17)
Infant sex
 Male 64 0.65 (0.40,1.29) 0.40 (0.25,0.79) 0.72 (0.40,1.52)
 Female 64 0.54 (0.37,0.89) 0.38 (0.20,0.65) 0.57 (0.38,0.93)
  1. Abbreviations: TWA time-weighted average
  2. *Kruskal-Wallis Test: P < 0.05