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Table 4 Association between individual exposure to ambient NO2 in different time periods during pregnancy and Small for Gestational Age (SGA).*

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

  SGA - weight
(n: 785)
SGA - length
(n:784)
NO2 exposure period OR (95% CI) Linearity (df)a OR (95% CI) Linearity (df)a
Unadjusted       
First trimester 1.013 (0.992; 1.035) L 1.001 (0.968; 1.035) L
Second trimester 1.013 (0.992; 1.034) L 1.006 (0.972; 1.041) L
Third trimester 1.004 (0.983; 1.026) L 1.013 (0.979; 1.049) L
Whole pregnancy 1.014 (0.988; 1.040) L 1.010 (0.970; 1.052) L
Adjusted b       
First trimester 1.182 (0.894; 1.563) L 1.137 (0.741; 1.744) L
Second trimester 1.369 (1.013; 1.849) L 1.416 (0.890; 2.254) L
Third trimester 1.186 (0.906; 1.552) L 1.103 (0.750; 1.623) L
Whole pregnancy 1.281 (0.942; 1.743) L 1.230 (0.778; 1.945) L
  1. *Estimates are expressed as the change in odds for SGA (birth weight) and SGA (birth length) 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 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).
  3. b Adjusted for:
  4. -SGA in weight: maternal age, maternal pre-pregnancy weight, paternal height, gestational weight gain, parity, maternal education, country of origin, smoking during pregnancy, and season of last menstrual period.
  5. -SGA in length: maternal age, maternal pre-pregnancy weight, maternal education, parity, smoking during pregnancy, gestational weight gain, country of origin, alcohol consumption during pregnancy, and season of last menstrual period.