Table 3.

Adjusted odds ratios (aOR) for the association between term low birth weight and average household ${\mathrm{NO}}_3^{-}$ concentrations over the pregnancy.

	Low birth weight
		$n=852,348$
${\mathrm{NO}}_3^{-}$ (mg/L)	$n$	aOR (95% CI)	$p$-Value
Categorical
$\le 1$	186,182	Ref (1)
$>1–\le 2$	182,870	0.98 (0.92, 1.05)	0.52
$>2–\le 5$	299,468	1.01 (0.94, 1.08)	0.86
$>5–\le 25$	150,019	1.02 (0.95, 1.09)	0.55
$>25$	33,809	0.99 (0.88, 1.12)	0.91
Trend	—b	—b	0.51
Continuousa	852,348	1.02 (0.93, 1.11)	0.73

Note: Models were fitted using logistic regression with generalized estimating equations to control for the nonindependence of births from the same mother and were controlled for maternal age, calendar year, sex, gravidity, maternal smoking, maternal education, maternal income, maternal employment status, region, and urbanicity. aOR, adjusted odds ratio; CI, confidence interval; Ref, reference.

^aContinuous ${\mathrm{NO}}_3^{-}$ exposure was log transformed, ln($\mathrm{x}+1$) and aOR (95% CI) shown for exposures $x=25.0\text{\hspace{0.17em}mg}/\mathrm{L}$ ${\mathrm{NO}}_3^{-}$ compared with $0\text{\hspace{0.17em}mg}/\mathrm{L}$.

^bThe empty cells correspond to the p-for-trend analyses and so there is no point estimate or 95% CI.