Prevalence of vitamin D deficiency in the pregnant women: an observational study in Shanghai, China

Background Maternal vitamin D deficiency has been a worldwide concern in recent years. However the epidemiological data of vitamin D deficiency among large group of Chinese pregnant women is limited. This study is to evaluate the prevalence of vitamin D deficiency among pregnant women in Shanghai, China and to analyze the association of vitamin D status with some pregnancy outcomes (gestational diabetes and low birth weight). Methods A total of 34,417 pregnant women in Shanghai were included in this study from January 2014 to December 2017, and the serum 25-hydroxyvitamin D [25(OH)D] concentrations were measured at 16th week of gestation by electrochemiluminescence assay. Seventy five grams of glucose was used to conduct oral glucose tolerance test during 24-28th week of gestational in all enrolled persons and the birth weight of newborns was recorded. Results The median serum 25(OH) D concentration in the pregnant women during 4 years was 42.87 nmol/L (32.88-51.90 nmol/L). 9.9% of the population were severe vitamin D deficient [25(OH)D < 25 nmol/L], 60.1% were deficient [25 nmol/L <= 25(OH)D < 50 nmol/L], 28.4% were insufficient [50 nmol/L <= 25(OH)D < 75 nmol/L] and only 1.6% of the enrolled population reached the level of adequate [25(OH)D >= 75 nmol/L]. Serum 25(OH) D concentrations showed significant difference among seasons with the highest level in winter and the lowest level in summer. Women with advanced maternal age were more likely to have better vitamin D status compared with younger women. The 25(OH) D levels were significantly different among 2014-2017. The year of 2017 had the highest 25(OH) D level with the median serum concentration reaching 47.80 nmol/L (41.00-55.00 nmol/L), while the lowest appeared in 2016 which has median 25(OH) D concentration at 38.87 nmol/L (28.76-49.97 nmol/L). No relations were found between the 25(OH) D status and the rate of gestational diabetes or low birth weight of newborns. Conclusion Pregnant women in Shanghai were generally deficient in vitamin D status and the level of vitamin D was related to season and age. No evidence showed vitamin D deficiency in pregnant women contributes to the rate of gestational diabetes or low birth weight of newborns in this study. These results suggest that most of the pregnant women may need vitamin D supplementation to achieve adequate vitamin D level.