This study was conducted to observe the prevalence of vitamin D deficiency during pregnancy and the effects of maternal 25-hydroxy-vitamin D (25-[OH]D) levels on fetal bone growth.

Five hundred twenty-three Korean pregnant women were randomly recruited and serum 25-(OH)D level was measured. During pregnancy, fetal ultrasonography and serum 25-(OH)D measurements were carried out 3 times in 275 of 523 pregnant women. Fetal biparietal and occipitofrontal diameter, head and abdominal circumference, and femur and humerus length were measured through fetal ultrasonography.

The prevalence of vitamin D deficiency (25-[OH]D<20 ng/mL) based on the 1st serum measurement of 25-(OH)D was 88.9%. There was no association between maternal serum 25-(OH)D level and fetal bone growth. In 275 pregnant women who completed study design, the mean value of 25-(OH)D was 12.97±5.93, 19.12±9.82, and 19.60±9.98 ng/mL at 12 to 14, 20 to 22, and 32 to 34 weeks of pregnancy, respectively and there was an association between the difference of serum 25-(OH)D level between 12 to 14 and 20 to 22 weeks and growth velocity of fetal biparietal diameter between 20 to 22 and 32 to 34 weeks of pregnancy.

This study shows a high prevalence of vitamin D deficiency in Korean pregnant women and the change of serum 25-(OH)D levels is related with the growth of fetal biparietal diameter, however other parameters are not associated with serum 25-(OH)D levels.