Extremely premature children benefit from specific follow-up that requires high nutritional intake and the use of specific therapies that expose them to the risk of nephrocalcinosis. Other identified risk factors are extreme prematurity and intrauterine growth restriction.

The incidence of nephrocalcinosis in very premature infants is unclear, ranging from 7 to 64%. Most studies are observational and only few case-control studies can properly analyse the risk factors for nephrocalcinosis in significant populations that include only preterm infants.

This nephrocalcinosis of prematurity regresses spontaneously in more than half of the cases, but has been associated with a risk of long-term complications: impaired renal function, high blood pressure, etc. This is an aggravating factor in the context of prematurity, which has been associated with an increased risk of renal impairment and hypertension in childhood and adulthood.

For all these reasons, nutritional intakes and therapeutics are monitored very closely and a renal ultrasound is routinely performed at discharge at 35 weeks of corrected gestational age in all children who are born at a gestational age ≤ 32 weeks and/or birth weight ≤ 1500 g.

Inclusion Criteria:

• Newborns with a gestational age <= 32 weeks and/or birthweight <=1500g

Exclusion Criteria:

• Newborns with kidney malformation

Infants born at the Croix-Rousse Hospital, Lyon, France between 01/01/2012 and 31/12/2017 with a gestational age <= 32 weeks and/or a birthweight <=1500g. Infants with a diagnosed kidney malformation are excluded.