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Table 3 Relative risks for term low birth weight according to trimester-specific exposure to air pollutants.

From: The association between low level exposures to ambient air pollution and term low birth weight: a retrospective cohort study

   Unadjusted* RR (95% CI) Adjusted** RR (95%CI) Adjusted for Birth Year*** RR (95%CI)
  1 st Trimester
O3
  < 25th percentile (referent)
  25 – 50th percentile 1.15 (0.89, 1.50) 1.16 (0.88, 1.53) 1.11 (0.83, 1.47)
  51 – 75th percentile 1.11 (0.85, 1.45) 1.04 (0.79, 1.37) 1.02 (0.77, 1.36)
  > 75th percentile 1.06 (1.80, 1.40) 1.01 (0.75, 1.35) 1.00 (0.74, 1.34)
  Continuous**** 1.01 (0.90, 1.14) 0.98 (0.86, 1.11) 0.98 (0.86, 1.12)
SO2
  < 25th percentile (referent)
  25 – 50th percentile 0.93 (0.71, 1.22) 0.96 (0.73, 1.28) 0.98 (0.74, 1.31)
  51 – 75th percentile 1.15 (0.87, 1.52) 1.18 (0.88, 1.58) 1.12 (0.84, 1.50)
  > 75th percentile 1.30 (1.00, 1.67) 1.36 (1.04, 1.78) 1.26 (0.96, 1.66)
  Continuous**** 1.17 (1.02, 1.33) 1.20 (1.05, 1.38) 1.15 (1.00, 1.31)
PM10
  < 25th percentile (referent)
  25 – 50th percentile 1.24 (0.95, 1.62) 1.24 (0.94, 1.64) 1.14 (0.86, 1.52)
  51 – 75th percentile 1.25 (0.96, 1.62) 1.24 (0.95, 1.64) 1.08 (0.82, 1.44)
  > 75th percentile 1.28 (1.00, 1.65) 1.33 (1.02, 1.74) 1.11 (0.84, 1.48)
  Continuous**** 1.09 (1.00, 1.18) 1.09 (1.00, 1.19) 1.03 (0.94, 1.14)
  2 nd Trimester
O3
  < 25th percentile (referent)
  25 – 50th percentile 0.99 (0.76, 1.30) 0.93 (0.70, 1.23) 0.90 (0.67, 1.20)
  51 – 75th percentile 1.13 (0.87, 1.45) 1.07 (0.82, 1.40) 1.07 (0.81, 1.41)
  > 75th percentile 1.01 (0.76, 1.33) 0.98 (0.73, 1.31) 0.98 (0.73, 1.30)
  Continuous**** 1.03 (0.92, 1.17) 1.03 (0.91, 1.18) 1.04 (0.91, 1.18)
SO2
  < 25th percentile (referent)
  25 – 50th percentile 1.14 (0.89, 1.47) 1.12 (0.86, 1.46) 1.14 (0.88, 1.49)
  51 – 75th percentile 1.05 (0.80, 1.37) 1.13 (0.85, 1.50) 1.09 (0.82, 1.45)
  > 75th percentile 0.92 (0.71, 1.20) 1.04 (0.79, 1.37) 0.99 (0.75, 1.32)
  Continuous**** 0.93 (0.82, 1.05) 0.99 (0.87, 1.13) 0.97 (0.85, 1.11)
PM10
  < 25th percentile (referent)
  25 – 50th percentile 0.98 (0.76, 1.28) 1.02 (0.77, 1.34) 0.99 (0.75, 1.31)
  51 – 75th percentile 1.09 (0.84, 1.40) 1.16 (0.89, 1.51) 1.10 (0.84, 1.45)
  > 75th percentile 1.00 (0.77, 1.28) 1.09 (0.83, 1.42) 1.01 (0.76, 1.34)
  Continuous**** 1.00 (0.91, 1.09) 1.02 (0.93, 1.12) 1.00 (0.90, 1.10)
  3 rd Trimester
O3
  < 25th percentile (referent)
  25 – 50th percentile 0.85 (0.64, 1.13) 0.89 (0.66, 1.19) 0.86 (0.64, 1.16)
  51 – 75th percentile 0.94 (0.72, 1.22) 0.95 (0.72, 1.25) 0.94 (0.71, 1.25)
  > 75th percentile 0.89 (0.67, 1.18) 1.01 (0.75, 1.36) 1.03 (0.76, 1.38)
  Continuous**** 0.94 (0.83, 1.07) 1.00 (0.87, 1.15) 1.01 (0.88, 1.16)
SO2
  < 25th percentile (referent)
  25 – 50th percentile 1.05 (0.82, 1.34) 1.04 (0.80, 1.34) 1.03 (0.80, 1.34)
  51 – 75th percentile 0.80 (0.60, 1.07) 0.85 (0.63, 1.15) 0.81 (0.60, 1.10)
  > 75th percentile 0.87 (0.68, 1.13) 0.88 (0.67, 1.15) 0.82 (0.63, 1.08)
  Continuous**** 0.91 (0.80, 1.03) 0.93 (0.81, 1.06) 0.89 (0.78, 1.02)
PM10
  < 25th percentile (referent)
  25 – 50th percentile 0.93 (0.72, 1.20) 0.96 (0.73, 1.26) 0.92 (0.70, 1.21)
  51 – 75th percentile 1.07 (0.83, 1.37) 1.14 (0.88, 1.48) 1.04 (0.80, 1.36)
  > 75th percentile 0.92 (0.71, 1.18) 1.03 (0.79, 1.35) 0.92 (0.69, 1.22)
  Continuous**** 0.95 (0.87, 1.05) 0.99 (0.89, 1.09) 0.94 (0.85, 1.05)
  1. * Unadjusted model has only air pollution and no other covariates
  2. ** Adjusted for gender of infant, gestational age, maternal age, parity, smoking during pregnancy, weight change, prior neonatal deaths, prior stillbirth, prior low birth weight and neighborhood family income.
  3. *** Adjusted for birth year, gender of infant, gestational age, maternal age, parity, smoking during pregnancy, weight change, prior neonatal deaths, prior stillbirth, prior low birth weight and neighborhood family income.
  4. **** RR for continuous model based on inter quartile range