Vitamin D nutrient status during pregnancy and its influencing factors

Little is known about variation of vitamin D (VD) status during pregnancy among Chinese women. This study is to assess the change of VD status during pregnancy and its influencing factors among Chinese women.

A running cohort study has being conducted in southeast China. The pregnant women were interviewed and the peripheral blood samples were collected at the first (T1), second (T2) and third trimester (T3), respectively. 25(OH)D₂ and 25(OH)D₃ were measured by liquid chromatography tandem-mass spectrometry. Multiple linear and logistic regression models were applied to explore the associations of VD supplement with 25(OH)D concentration and VD deficiency, respectively.

There were 4368 pregnant women enrolled in the current study. The 25(OH)D concentration increased notably with gestational week. The average plasma 25(OH)D concentration in T1, T2 and T3 was 18.94 ± 8.74, 23.05 ± 11.15, and 24.65 ± 11.59 ng/mL, respectively. Correspondingly, VD deficiency (25(OH)D < 20 ng/mL) rate was 65.26%, 33.56% and 32.12%. In T1 phase, higher pre-pregnancy BMI, more parity, sampling in summer/autumn were related to higher 25(OH)D level, and similar patterns were observed in T2 and T3 phase. There was positive dose-response effect between VD supplement frequency and 25(OH)D concentration during pregnancy, adjusting for potential confounders (T1: β(SE) = 3.907 (0.319), P < 0.001; T2: β(SE) = 2.780 (0.805), P < 0.001; T3: β(SE) = 3.640 (1.057), P = 0.006). Not surprisingly, supplementing VD > 3 times/week reduced the risk of VD deficiency during pregnancy significantly, compared to without VD supplement (T1: OR = 0.30, 95% CI: 0.24-0.37; T2: 0.56, 0.38-0.82; T3: 0.67, 0.44-0.96).

VD level increased with gestational week among Chinese pregnant women. High frequency of VD supplement during pregnancy is an effective way to reduce risk of VD deficiency, especially among the pregnant women with younger age, low prepregnancy BMI and primipara, and during winter and spring season.