Table 2.

Association between maternal 25-hydroxyvitamin D (25(OH)D) at ≤26 weeks and preeclampsia, mild preeclampsia, and severe preeclampsia, Collaborative Perinatal Project (1959–1965)

Maternal serum 25(OH)D, nmol/L	Cases (n)	Unadjusted Incidencea	Unadjusted risk difference (95% CI)	Adjustedb risk difference (95% CI)	Unadjusted risk ratio (95% CI)	Adjustedb risk ratio (95% CI)
Preeclampsia (mild and severe)
<30	185	.028	ref	ref	ref	ref
30-<50	247	.027	−.0009 (−.006, .005)	.001 (−.003, .006)	.97 (.78, 1.2)	1.1 (.84, 1.3)
50-<75	171	.022	−.005 (−.011, −.0001)	−.002 (−.006, .003)	.79 (.63, .99)	.90 (.69, 1.2)
≥75	114	.026	−.002 (−.008, .005)	.002 (−.004, .008)	.93 (.71, 1.2)	1.1 (.89, 1.5)
1-standard deviation c increase			−.002 (−.004, .0003)	.002 (−.015, .010)	.93 (.85, 1.0)	.99 (.89, 1.1)
Mild preeclampsia
<30	144	.022	ref	ref	ref	ref
30-<50	179	.020	−.002 (−.006, .003)	0 (−.003, .003)	.91 (.72, 1.2)	1.0 (.77, 1.3)
50-<75	137	.018	−.004 (−.009, .001)	−.001 (−.004, .002)	.80 (.62, 1.0)	.92 (.69, 1.2)
≥75	100	.023	.001 (−.005, .007)	.003 (−.001, .007)	1.0 (.79, 1.4)	1.3 (.90, 1.7)
1-standard deviation c increase			−.0004 (−.002, .001)	.003 (−.007, .012)	.98 (.89, 1.1)	1.0 (.93, 1.2)
Severe preeclampsia
<30	41	.0063	ref	ref	ref	ref
30-<50	68	.0076	.001 (−.002, .004)	.003 (−.002, .008)	1.2 (.76, 1.7)	1.3 (.86, 2.0)
50-<75	34	.0045	−.002 (−.004, .001)	−.001 (−.006, .003)	.74 (.46, 1.2)	.87 (.87, 1.4)
≥75	14	.0032	−.003 (−.006, −.0004)	−.003 (−.009, .003)	.51 (.27, .96)	.69 (.32, 1.4)
1-standard deviation c increase			−.002 (−.003, −.0006)	−.002 (−.003, .0002)	.73 (.61, .90)	.79 (.62, .99)

^aIncidence is based on the weighted sample.

^bAdjusted for maternal race, prepregnancy body mass index, parity, socioeconomic status, smoking status, latitude of study site, season of blood sampling, gestational age at blood sampling, and trimester of entry to prenatal care.

^c1 SD is 28 nmol/L.