A Prospective Study of Nephrocalcinosis in Very Preterm Infants: Incidence, Risk Factors and Vitamin D Intake in the First Month

<i>Background and objectives</i>: Nephrocalcinosis (NC) is a common condition characterized by the deposition of calcium salts in the kidneys of very preterm infants due to tubular immaturity, intensive treatment and nutritional supplements. However, optimal vitamin D supplementation remains unclear. In most patients, NC spontaneously resolves within the first year of life, but long-term kidney function data are lacking. The aim was to study nephrocalcinosis in very preterm infants, assess risk factors and evaluate vitamin D's impact during the first month with a 2-year follow-up. <i>Material and Methods</i>: This was a prospective observational study conducted over a 3-year period in infants with a gestational age of less than 32 weeks. The patients' data were compared between the NC and control groups based on kidney ultrasound results at discharge. In the first month, the mean vitamin D intake from all sources as well as biochemical markers of calcium metabolism were collected. Patients diagnosed with NC were referred to a pediatric nephrologist after discharge. <i>Results</i>: NC was found in 35% of a cohort of 160 infants, more common in those with a gestational age <28 weeks. Risk factors were associated with higher morbidity and necessary treatment. At 28 days, serum 25-hydroxy vitamin D levels differed between NC and control groups (<i>p</i> < 0.05). The NC group with GA ≥ 28 weeks had higher vitamin D intake (<i>p</i> < 0.05), hypercalciuria and calcium/creatinine ratio (<i>p</i> < 0.01) and lower parathyroid hormone levels (<i>p</i> < 0.05). Follow-up showed resolution in 70% at 12 months and 90% at 24 months. <i>Conclusions</i>: The prevalence of NC in very preterm infants is significant, associated with lower maturity and higher morbidity. Careful vitamin D supplementation and biochemical monitoring of Ca metabolism from the first month of life should support bone health and limit the risk of nephrocalcinosis. Due to the high incidence of NC in very preterm infants, long-term follow-up is essential.