 AKI is associated with morbidity and mortality in critically ill neonates. The risk of AKI is higher in very low birth weight infants requiring assisted ventilation and ionotropic support, and in infants with congenital heart disease. Additionally, AKI occurs more frequently in infants who suffered severe birth asphyxia. While it has been established that end-stage kidney disease ESKD is associated with worsening sleep apnea in adults, it has been proposed that sleep apnea and nocturnal hypoxemia may contribute to kidney injury, the development of chronic kidney disease CKD, and the progression to kidney failure. Proposed mechanisms of kidney disease via intermittent nocturnal hypoxemia include 1: direct intrarenal hypoxemia resulting in tubulointerstitial injury 2: an increase in oxidative stress, inflammatory cytokines, and systemic blood pressure via activation of the renin-angiotensin system. Hence It is plausible that IH may modulate AKI in preterm neonates. The investigators goal is to test the hypothesis that intermittent hypoxemia is associated with Acute Kidney Injury in preterm infants. Investigation of relationship between IH and AKI may provide further insight into onset and prevention given the recent advancements in the detection and characterization of AKI in this vulnerable population. 