Objectives: Vitamin D deficiency during pregnancy can increase the risk of pre-eclampsia, diabetes and high blood pressure. Therefore, it is needed to determine vitamin D deficiency rate and related factors in pregnant women of the first trimester.

Methodology: A cross-sectional study was conducted from November 2015 to March 2016. The study subjects were pregnant women of the first trimester who were randomly and singly selected from those visiting the antenatal care clinic of Hung Vuong Hospital. Vitamin D deficiency is defined as 25(OH)D blood concentration ≤ 20 ng/mL (or 50 nmol/L). We used blood samples routinely taken in the first trimester of pregnancy to quantify 25(OH)D. Other information was collected through on-site interview with pregnant women based on a prepared questionaire.

Results: Vitamin D deficiency rate was 31.09 percent on 386 samples. Vitamin D deficiency in pregnant women had a statistically significant correlation with such factors as pregnant women aged 20-25 years versus adolescent group (PR=0.5), non-King group (PR=2.01), poor economic status group (PR=2.60), those with more than two pregnancies (PR=0.45), those with severe morning sickness (PR=1.68), those with weight gain in the first trimester
(PR=0.70), those working outdoors (PR=0.58).

Conclusion: Healthcare providers need to counsel pregnant women right at the first antenatal care visit to prevent and minimise vitamin D deficiency during pregnancy in order to reduce risks for pregnant women and foetuses.