Table 3. Association between maternal 25(OH)D concentration and the risk of preterm birth by preterm birth subtype.

	Spontaneous Preterm Birth Rates	Spontaneous Preterm Birth: OR	Indicated Preterm Birth Rates	Indicated Preterm Birth: OR
	(<37 Weeks)	(95% CI)	(<37 Weeks)	(95% CI)
<20 ng/mL (N = 248)	21 (8%)	1.0	28 (11%)	1.0
N preterm (%)
20 to <30 ng/mL (N = 267)	17 (6%)	0.74	16 (6%)	0.50
N preterm (%)		(0.38, 1.43)		(0.26, 0.95)
30 to <40 ng/mL (N = 255)	16 (6%)	0.72	16 (6%)	0.53
N preterm (%)		(0.37, 1.42)		(0.28, 0.99)
≥40 ng/mL (N = 294)	11 (4%)	0.42	14 (5%)	0.39
N preterm (%)		(0.20, 0.89)		(0.20, 0.76)

Bold values signify significance at p<0.05.