Respiratory distress syndrome (RDS) of the newborn, also called as hyaline membrane disease, is the most common cause of respiratory distress in premature infants, correlating with structural and functional lung immaturity. The pathophysiology of RDS is complex. Immature type II alveolar cells produce less surfactant that causes an increase in alveolar surface tension and a decrease in compliance. This resultant atelectasis lead to pulmonary vascular constriction, hypoperfusion, and lung tissue ischemia. RDS and prolonged ventilation and associated systemic/lung injury may also contribute to long term oxygen dependency and may result in bronchopulmonary dysplasia (BPD). Vitamin D is a fat-soluble steroid hormone that primarily contributes to the maintenance of normal calcium homeostasis and skeletal mineralization. In addition to its classical role in bone metabolism, vitamin D deficiency has been associated with impaired pulmonary function, increased incidence of viral and bacterial infections and inflammatory lung diseases. Although exact mechanisms are not fully understood, vitamin D appears to impact on a variety of inflammatory and structural cells within the lung including macrophages, lymphocytes and epithelial cells. To our best of knowledge, no study has evaluated the effect of vitamin D levels on the severity and presence of RDS in preterm infants. Therefore, the aim of this study is to evaluate the possible role of maternal/neonatal vitamin D levels on RDS development in preterm infants. We also aim to determine the possible association between maternal/neonatal vitamin D levels and the incidence of BPD and other neonatal morbidities.

Preterm infants with respiratory distress who are <37 weeks of gestational age and will be admitted to Neonatal Intensive Care Unit of Kanuni Sultan Suleyman Training and Research Hospital will be included in this prospective study. Blood for neonatal and maternal vitamin D levels will be obtained from all infants and their mothers at the time of hospital admission. The infants will be evaluated for RDS and surfactant requirement. If they have RDS and need of mechanical ventilation, they will be intubated and given surfactant, if necessary. The maternal and neonatal demographics of infants will be recorded. Infants will also be followed up in terms of other morbidities including patent ductus arteriosus, necrotizing enterocolitis, retinopathy of prematurity, and especially BPD. Then infants will be divided into three groups according to maternal/neonatal vitamin D levels (mild, moderate and severe vitamin D deficiency) and group comparisons will be performed Plasmas after separated and stored at -80 C. Levels of 25-OHD will be determined using Shimadzu LC-20AT model High Performance Liquid Chromatography (HPLC) system. Data will be analyzed using SPSS software and appropriate statistical analyses will be performed.

Inclusion Criteria:

• Preterm infants <37 weeks of gestational age and are admitted to Neonatal Intensive Care Unit of Kanuni Sultan Suleyman Training and Research Hospital
• Preterm infants with clinical and laboratory findings of RDS

Exclusion Criteria:

• presence of maternal clinical and/or histological chorioamnionitis,
• presence of premature rupture of membranes (PROM),
• refusal of parental consent,
• lack of laboratory data,
• major congenital abnormalities

Premature infants admitted to neonatal intesive care unit with the diagnosis of respiratory distress syndrome (RDS) will constitute the RDS group, whereas preterm infants without RDS will constitute the non-RDS group