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Table 2 Association between individual exposure to ambient NO2 in different time periods during pregnancy and anthropometric measures at birth.*

From: Air pollution exposure during pregnancy and reduced birth size: a prospective birth cohort study in Valencia, Spain

  Birth weight (in g)a
(n:785)
Birth length (in cm)a
(n:784)
Birth head circumference (in cm)a
(n:782)
NO2 exposure period β (95% CI) Linearity (df)b β (95% CI) Linearity (df)b β (95% CI) Linearity (df)b
Unadjusted          
First trimester -3.564 (-23.698;16.570) L -0.092 (-0.177;-0.008) NL (4) -0.069 (-0.133;-0.004) L
Second trimester -4.464 (-25.175;16.248) NL (3) -0.050 (-0.137;0.037) NL (2) -0.071 (-0.137;-0.004) L
Third trimester -5.740 (-26.553;15.072) L -0.010 (-0.096;0.077) NL (4) -0.017 (-0.084;0.049) L
Whole pregnancy -5.792 (-30.065;18.481) NL (3) -0.063 (-0.165;0.038) L -0.074 (-0.152;0.003) L
Adjusted c          
First trimester -12.782 (-34.537;8.972) NL (3) -0.066 (-0.149;0.017) NL (4) -0.066 (-0.137;0.005) L
Second trimester -9.961 (-32.594;12.671) NL (4) -0.040 (-0.125;0.044) NL (3) -0.060 (-0.133;0.014) NL (3)
Third trimester -4.294 (-25.923;17.335) L -0.005 (-0.089;0.079) NL (2) -0.028 (-0.099;0.042) L
Whole pregnancy -9.729 (-33.218;13.760) L -0.047 (-0.146;0.052) NL(2) -0.058 (-0.134;0.018) NL (3)
  1. * Estimates are expressed as the change in birth anthropometric measures for a 10 μg/m3 increase in the mean NO2 levels at each woman's residence during the corresponding period. Unadjusted and adjusted models.
  2. a Standardized for gestational age.
  3. b Shape of the relationship after contrast between model with NO2 in non-linear vs. linear form; L: linear; NL: non-linear (and degrees of freedom of the selected model).
  4. c Adjusted for:
  5. -Birth weight = maternal age, maternal pre-pregnancy weight, maternal height, paternal height, gestational weight gain, parity, maternal education, smoking during pregnancy, country of origin, sex of the infant, and season of last menstrual period.
  6. -Birth length = maternal age, maternal height, gestational weight gain, parity, maternal education, smoking during pregnancy, working status in the first trimester, country of origin, and sex of the infant.
  7. -Birth head circumference: maternal age, maternal pre-pregnancy weight, maternal height, gestational weight gain, parity, maternal education, smoking during pregnancy, country of origin, sex of the infant, and season of last menstrual period.