Table 2.

The association between vitamin D concentration in the first trimester, conception season, and risk of GDM.

Variable	Crude OR (95% CI)	Adjusted OR1 (95% CI)	Adjusted OR2 (95% CI)	Adjusted OR3 (95% CI)
Vitamin D
Normal	1.00	1.00	1.00	1.00
Insufficiency	0.84 (0.59-1.20)	0.86 (0.59-1.26)	0.88 (0.60-1.29)	0.87 (0.55-1.27)
Deficiency	0.61 (0.44-0.84)	0.69 (0.49-0.98)	0.79 (0.55-1.13)	0.78 (0.54-1.11)
Conception season
Spring-summer	1.00	1.00	1.00	—
Fall-winter	0.59 (0.47-0.74)	0.61 (0.48-0.77)	0.63 (0.49-0.81)	—

Adjusted OR1 for vitamin D is adjusted for age, prepregnancy BMI, family history of diabetes, parity, smoking, drinking, gestational week of blood withdrawn, income, and education; adjusted OR1 for conception season is adjusted for age, prepregnancy BMI, family history of diabetes, parity, smoking, drinking, income, and education; adjusted OR2 for vitamin D is adjusted OR1 plus adjusting for conception season (as four categories); adjusted OR2 for conception season was adjusted OR1 plus adjusting for vitamin D (as three categories). Adjusted OR3 is adjusted OR1 plus the season of the blood draw (as four categories) in the first trimester. Abbreviations: BMI: body mass index; OR: odds ratio; CI: confidence interval.