. Author manuscript; available in PMC: 2017 Jan 6.

Published in final edited form as: J Steroid Biochem Mol Biol. 2015 Nov 10;155(Pt B):245–251. doi: 10.1016/j.jsbmb.2015.10.022

Table 2.

Association between serum 25(OH)D concentration within 6 weeks of delivery and the risk of preterm birth (nichd & trf, n=509)

	Preterm Birth (<37 Weeks)	Term Birth (≥37 Weeks)	p-value (test for trend)	Unadjusted RR (95% CI)	Adjusted^† RR (95% CI)
≤20 ng/mL N (%)	14 (17%)	68 (83%)	0.01	1.0	1.0
>20 to <40 ng/mL N (%)	19 (10%)	175 (90%)		0.57 (0.30, 1.09)	0.59 (0.31,1.14)
≥40 ng/mL N (%)	17 (7%)	216 (93%)		0.43 (0.22, 0.83)	0.41 (0.20, 0.86)

Bold values signify significance at p<0.05.

^†

Adjusted for race/ethnicity, maternal age, and insurance status.