Table 4

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

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

*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.

^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).

^b Adjusted for:

-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.

-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.

Ballester et al. Environmental Health 2010 9:6   doi:10.1186/1476-069X-9-6