In very low birth weight (<1500g) preterm infants, nutrition with mother's own milk, as opposed to formula, is associated with reduced morbidity and mortality. At present, the merits and risks of pasteurising mother's own milk (recommended if the mother is positive for cytomegalovirus) are unknown. This single-institution retrospective analysis aims at comparing mortality and morbidity of preterm infants below 1500g birth weight who were fed raw (unpasteurized) or pasteurized mother's own milk (in case the mother is positive for cytomegalovirus). The infant's sex into is taken into account as a possible confounder.

Retrospective analysis of preterm infants below 1500g birth admitted 2019-2024 to the Department of Neonatology at the Charité - Universitätsmedizin Berlin. Infants with major congenital malformation, chromosomal aberrrations and known genetic conditions are excluded. Input variables are basic demographic data (gestational age, birth weight, sex, antenatal steroids, and others), duration of mother's own milk feeding, duration of donor milk feeding, cytomegalovirus status of the mother, pasteurization of mother's own milk (start and end date), main outcome variables are death, major surgery, necrotizing enterocolitis, duration of antibiotic treatment, duration of positive pressure ventilation, duration of oxygen supplementation, duration of hospital treatment.

Inclusion Criteria:

- Preterm infants Birth weight below 1500g Admitted to Charité Universitätsmedizin Berlin Year of birth 2019-2024

Exclusion Criteria:

Major congenital malformations Chromosomal aberrations Known genetic conditions

Admitted to Charité Universitätsmedizin Berlin Year of birth 2019-2024

IPD sharing requires prior consent of the Ethikkommission der Charité - Universitätsmedizin Berlin