RESULTS
Of the 303 women who were enrolled, 237 had complete mother/umbilical cord blood data. 138 (47.7%) women had vitamin D deficiency (< 50nmol/L) at delivery whereas only 34 (13.8%) of the cord-blood samples showed levels under the recommended cut-off for newborns (< 30nmol/L) (10). The mean difference between maternal venous blood and cord blood 25(OH)D was negative (higher levels in the cord blood compared to the maternal blood) in 91% of cases (-16.27nmol/L, SD=13.36), Fig 1. The difference was not significantly associated with maternal 25(OH)D level, placenta weight or delivery mode (p > 0.493). After dividing the women into three groups, <25nmol/L (n=64), 25-49.9nmol/l (n=74) and ≥50nmol/L (n=151) we did not find significant difference in maternal age, gestational age at delivery, fetal weight, level of ionized calcium (Ca2+) in the cord blood, maternal body-mass-index (BMI), nationality, exposure to sunlight, frequency of diabetes or delivery mode, Table 1. Multiple regression with maternal 25(OH)D as the dependent variable and supplementation dose, age, BMI, nationality, education, exposure to sunlight, diabetes as independent variables showed that only the dose of supplementation (p <0.001) had a significant influence on maternal 25(OH)D, Table not shown.
The correlation between maternal and umbilical cord 25(OH)D was for the whole cohort 0.906 (p < 0.001). Subdivision into different levels of maternal 25(OH)D, delivery mode, diabetes and BMI showed a lower correlation coefficient for all three subgroups of maternal levels. For all other calculations the correlation was excellent (Table 2). There was no correlation between placenta weight or hematocrit to the umbilical cord level of 25(OH)D (r = 0.193, p = 0.180, respectively r = -0.063, p = 0.353).
The correlation between maternal and umbilical cord 25(OH)D was not to a clinical point of view affected by the supplementation dose (none supplementation n = 18, r = 0.948; 10.000UI/week n = 73, r = 0.853; 20.000UI/week n = 38, r = 0.805; all P values < 0.000). For those without information about supplementation (n = 106) the correlation coefficient was 0.938 (P < 0.000). The correlation between umbilical cord Ca2+ and supplementation dose was non-significant (n = 141, r = 0.000, p = 0.997).
The risk for preterm labor (OR 1.725, 95%CI: 0.808-3.683) preterm rupture of membranes (OR 1.538, 95%CI: 0.678-3.491), low AS (3.465, 95%CI 0.310-38.777) with 25(OH)D levels < 50nmol/L was not increased whereas the risk for diabetes was significantly decreased (OR 0.470, 95 CI 0.252-0.879).