Vitamin D during pregnancy: why observational studies suggest deficiency and interventional studies show no improvement in clinical outcomes? A narrative review

International audienc

The relationship between low maternal serum 25-hydroxyvitamin D levels and gestational diabetes mellitus according to the severity of 25-hydroxyvitamin D deficiency

OBJECTIVE: To assess the relationship between low maternal serum 25-hydroxyvitamin D levels and gestational diabetes mellitus in Turkish pregnant women according to the severity of 25-hydroxyvitamin D deficiency and assess intact parathyroid hormone levels in women with gestational diabetes mellitus and controls with low and sufficient 25-hydroxyvitamin D levels. METHODS: We analyzed serum 25-hydroxyvitamin D and intact parathyroid hormone levels in 234 women with gestational diabetes mellitus and 168 controls. To define the deficiency status, 25-hydroxyvitamin D levels were further classified into severely deficient, deficient, insufficient and sufficient groups. RESULTS: Women with gestational diabetes mellitus had significantly lower 25-hydroxyvitamin D levels compared to controls (30.8±16.3 vs. 36.0±16.2 nmol/L). However, when subgroups of 25-hydroxyvitamin D were analyzed, gestational diabetes mellitus was significantly more common only in women with severely deficient 25-hydroxyvitamin D levels. After adjusting for covariates, only severely deficient 25-hydroxyvitamin D levels were independently associated with an increased relative risk of gestational diabetes mellitus. The relative risk of gestational diabetes mellitus in women with insufficient and deficient 25-hydroxyvitamin D levels was not statistically significant. Intact parathyroid hormone concentrations were also significantly higher in women with gestational diabetes mellitus compared to the controls (45.3±26.2 vs. 38.7±27.6 pg/ml). CONCLUSIONS: The results obtained from this study provide novel data indicating that only severely deficient maternal serum 25-hydroxyvitamin D levels are significantly associated with an elevated relative risk of gestational diabetes mellitus, even after adjusting for established risk factors of gestational diabetes mellitus

Low vitamin D and risk for small for gestation age babies in gestational diabetes

This study aims to find the possible correlation of vitamin D with the onset of gestational diabetes mellitus (GDM) and its effect on fetal growth. A case-control study was conducted recruiting pregnant women in their second trimester. All subjects were classified as per the guidelines of the International Association of Diabetes and Pregnancy Study Groups (IADPSG) criterion. Fetal growth scans were recorded at 28th week of gestation. Venous blood was collected and serum levels of 25-(OH) D, Calcium, TNF alpha were measured. Vitamin D concentration in cases was lower (2.40 ± 1.10 ng/ml) as compared to controls (5.50 ± 1.74 ng/ml), while serum calcium levels of both groups were under normal range. TNF alpha level in cases was higher as compared to controls (p \u3c 0.001). On ultrasound scan, 47% of the babies of GDM mothers were small for gestational age. No difference was observed in terms of femur length and fetal weight in both groups (p \u3e 0.05). Weak negative correlation of vitamin D with insulin resistance (r = −0.304; p = 0.004), positive correlation with fetal growth (r = 0.303; p = 0.043) and a strong negative correlation with TNF alpha levels (r = −0.703; p = 0.023) were observed. Low vitamin D levels may be associated with the onset of gestational diabetes and affect fetal growth and development. Hence, antenatal screening and timely intervention is recommended