Changes in calcium, vitamin D, and other biochemical factors during pregnancy

Calcium and vitamin D play major roles in calcium homeostasis and skeletal development, especially during pregnancy. This study was conducted to determine serum constituents related to calcium metabolism of pregnant women as compared to non-pregnant ones. In a cross sectional study, 48 pregnant women from 5 prenatal care centers, and 66 non-pregnant women randomly selected from the Tehran Lipid and Glucose Study population were enrolled in the study. A questionnaire was used to obtain demographic information for both groups. Venous blood samples were taken to measure serum calcium, phosphorus, magnesium, alkaline phosphatase, albumin, parathyroid hormones, 25-OH vitamin D and serum osteocalcin levels. The repeated measure procedure and Dunnett test were used for statistical analysis. Data were adjusted for age in both case and control groups. Significant differences were found in the mean serum levels of albumin, osteocalcin and alkaline phosphatase between three trimesters of pregnancy (P<0.001). These differences were also significant in comparison to the control group. The mean values of albumin were 4.8±0.3, 4.3±0.3, 4.4±0.4, and 5.0±2 in the first, second and third trimesters and the control group respectively. These values for osteocalcin were 12.7±8.5, 8.1±6.7, 5.6±5.0 and 15.3±9.4 respectively and those for alkaline phosphatase were 115±38, 125±37, 174±61 and 137±42 respectively. In the first trimester alkaline phosphatase and 25-OH vitamin D decreased and albumin, parathyroid hormone and osteocalcin increased. In the first trimester 20% and 40% had vitamin D<10 ng/ml and <20 ng/ml respectively. Significant changes in albumin, parathyroid hormone, osteocalcin and alkaline phosphatase are observed in pregnant women throughout pregnancy. Vitamin D decreases in the first trimester and 20% have vitamin D deficiency.