Changes in vitamin D status considering hemodilution factors in Japanese pregnant women according to trimester: A longitudinal survey

Objectives There have been no longitudinal surveys on the changes in 25-hydroxyvitamin D [25(OH)D] while considering hemodilution factors among pregnant Japanese women. Therefore, we examined 25(OH)D levels as well as red blood cell count (RBC), hemoglobin (Hb), and Hematocrit (Hct) at the three trimesters among pregnant Japanese women to determine the distribution of serum 25(OH)D levels and the influence of hemodilution. Design This was a longitudinal study. Setting The study was conducted at Ibaraki Seinan Medical Center Hospital in Japan. Participants The participants comprised 50 women in the first trimester with singleton pregnancies and without any complications. Outcome measures Participants were recruited from June to August 2018, and followed up till their postpartum period. Blood samples were collected at the first, second, and third trimesters, i.e., at 4-15, 16-27, and 28-39 weeks, respectively. 25(OH)D levels, RBC, Hb, and Hct were analyzed across the three trimesters. Results Comparing the first, second, and third trimesters, 25(OH)D, RBC, and Hb were significantly declined in the second and third trimesters (p < 0.001). According to Spearman's correlation coefficient with 25(OH)D and RCB, Hb, Hct, significant correlations were found between 25(OH)D and Hb (p < 0.001), as well as Hct (p < 0.001) in the third trimester. Conclusions The present study had two major findings. First, it showed that the vitamin D status of most pregnant Japanese women were considered as vitamin D deficient. Second, the maternal serum 25(OH)D levels, RBC, Hb, and Hct of the pregnant women declined in the second and third trimesters. Thus we propose to have routine screening of vitamin D status of pregnant women, especially in the second trimester.