Table 3.

Association Between Maternal Serum 25-Hydroxyvitamin D at 24–28 Weeks and Preterm Birth at Less Than 35 Weeks

Maternal 25- Hydroxyvitamin D	Preterm Birth Less Than 35 Weeks	Birth 35 Weeks or More	Pearson P	Unadjusted OR (95% CI)	Adjusted* OR (95% CI)
Less than 75 nmol/L	42 (49.4)	43 (50.6)		1.0 (ref)	1.0 (ref)
75 nmol/L or more	33 (26.2)	93 (73.8)	<0.001	0.4 (0.2, 0.7)	0.4 (0.2, 0.8)
Per onestandard deviation increase† (continuous)	n/a	n/a		0.5 (0.4,0.7)	0.5 (0.3, 0.8)
Quartile 1 (median 43.6 nmol/L)	27 (51.9)	25 (48.1)		1.0 (ref)	1.0 (ref)
Quartile 2 (median 72.7 nmol/l)	24 (45.3)	29 (54.7)	0.50	0.8 (0.4, 1.7)	1.0(0.4, 2.5)
Quartile 3 (median 95.4 nmol/L)	15 (28.3)	38 (71.7)	0.01	0.4 (0.2, 0.8)	0.4(0.2, 1.1)
Quartile 4 (median 116 nmol/L)	9 (17.0)	44 (83.0)	<0.001	0.2 (0.1, 0.5)	0.2 (0.1, 0.7)

OR, odds ratio; CI, confidence interval.

Data are n (%) unless otherwise specified.

^*Adjusted for maternal race-ethnicity, gestational age at blood draw, study site, parity, prepregnancy BMI, season of blood draw, smoking status, marital status, education, and 17 α-hydroxyprogesterone caproate treatment

^†One standard deviation is 31.5nmol/L.