Tehran University of Medical Sciences Journal of Family and Reproductive Health 1735-8949 15 2 2021 06 20 99 105 Ziba Mosayebi Maternal, Fetal and Neonatal Research Center, Tehran University of Medical Sciences, Tehran, Iran Setareh Sagheb Department of Neonatology, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran Mahsa Mirzendedel Children's Medical Center, Tehran University of Medical Sciences, Tehran, Iran Amir Hossein Movahedian Bahrami Children's Hospital, Tehran University of Medical Sciences, Tehran, Iran 2020 11 07 2021 04 04 Objective: Vitamin D deficiency is a major health problem in all age groups. In the present study, we aimed to determine the prevalence of vitamin D deficiency in neonates hospitalized in an intensive care unit (NICU) and its association with clinical neonatal outcomes. Materials and methods: A prospective cross-sectional study was carried out on all neonates hospitalized in the NICU of Children's Medical Center over a period of one year (January–December 2018). Immediately on admission, a serum sample for vitamin D measurement was obtained with another routine blood sampling. Demographic and clinical data including sex, gestational age, the season of birth, serum levels of vitamin D and calcium, the causes of hospitalization, age at admission and neonatal outcomes including length of hospital stay and mortality during hospitalization were assessed. Results: One hundred neonates entered the study. Vitamin D deficiency and insufficiency were present in 95% of neonates. There was a significant association between vitamin D status and birth during winter (p=0.014); hypocalcemia (p=0.025) and older age at NICU admission (p<0.001). The mean value of vitamin D in term neonates was significantly lower than in preterm neonates (p=0.031). There were no correlations between length of hospital stay and neonatal mortality rate with vitamin D status (p=0.876). Conclusion: Vitamin D deficiency and insufficiency were highly prevalent among NICU patients. Maternal vitamin D supplementation during pregnancy may prevent or reduce the risk of low levels of vitamin D in neonates. https://jfrh.tums.ac.ir/index.php/jfrh/article/view/1600 https://jfrh.tums.ac.ir/index.php/jfrh/article/download/1600/559