Abstract:Objective To investigate vitamin D level at birth and possible influencing factors in preterm infants. Methods A total of 600 preterm infants were enrolled, and venous blood samples were collected within 24 hours after birth to measure the serum level of 25-hydroxyvitamin D[25(OH)D]. The effect of sex, birth weight, birth season, gestational age, mother's age, body mass index (BMI) in early pregnancy, delivery mode, and complications during pregnancy on serum 25(OH)D level was analyzed. Results The rates of vitamin D defciency, insuffciency, and suffciency were 42.0%, 38.7%, and 19.3% respectively. The preterm infants born in summer and autumn had a signifcantly higher serum 25(OH)D level than those born in winter (P < 0.05) and a signifcantly lower incidence rate of vitamin D defciency than those born in spring and winter (P < 0.003). Compared with those whose mothers were aged < 30 years, the infants whose mothers were aged ≥ 30 years had a signifcantly higher serum 25(OH)D level (P < 0.05) and a signifcantly lower incidence rate of vitamin D defciency (P < 0.017). Compared with those whose mothers were overweight or had normal body weight, the infants whose mothers were obese had a signifcantly lower serum 25(OH)D level (P < 0.05) and a signifcantly higher incidence rate of vitamin D defciency (P < 0.006). Compared with those whose mothers had no preeclampsia, the infants whose mothers had preeclampsia during pregnancy had a signifcantly lower serum 25(OH)D level (P < 0.05) and a signifcantly higher incidence rate of vitamin D defciency (P < 0.017). The multivariate analysis showed that birth in winter and spring, mother's age < 30 years, and early-pregnancy BMI ≥ 28 kg/m2 were risk factors for vitamin D defciency (P < 0.05). Conclusions There is a high prevalence of vitamin D defciency in preterm infants. Vitamin D supplementation should be given to the preterm infants with high-risk factors for vitamin D defciency.