Investigation about the effect on weight gain in extremely low birth weight preterm with individualized fortification, according to human milk analysis versus fortification adjusted according to urea serum concentration.

1. Study design This is an interventional, randomized, controlled study.

2. Description of the study The very premature newborn will be identified by daily evaluation of the infants admitted for consultation in the income book.

   Informed consent will be requested from the infant´s father, mother or legal guardian between the fifth and tenth day of life.

   Fortification will be done according to the randomization group.

3. Outline of the study design

   • Excel calculation sheet of individualized supplementation according to the composition of breast milk in the target fortification group. Methodology of analysis of breast milk in FOSS analyzer.

   • In the adjusted fortification group, urea concentration levels will be kept between 19-30 mg / dL

   • Fenton curves or https://www.growthcalculator.org/ will be used for Z-scores calculation.

   • Growth speed calculation: Weight gain: (1000x ln [Final weight / Initial weight]) / number of days.

     4 Duration of the study for each participant The duration of participation in the study and the fortification intervention period will be a maximum of 132 days.

Inclusion Criteria:

1. Preterm infants born <1000 g of birth weight that are fed with breast milk or donated milk.
2. Written informed consent signed by the mother, father or legal guardian.
3. To tolerate enteral feeding, at least 100mL / kg / day.

Exclusion Criteria:

1. Non-premature or premature patients weighing ≥ 1000 gr.
2. Patients with major malformations.
3. Patients with diagnosed chromosomal diseases or of high diagnostic suspicion.
4. Patients with short bowel syndrome or any surgery on the gastrointestinal tract.

Individual participant data underlying the results reported in this article after deidentification (text, tables, figures and appendices) will be available upon request. Data will be available 3 months to 5 years after publication of the article. Other documents will be available: study protocol, informed consent form. Researchers submitting a methodologically sound proposal should contact miguel.saenz@salud.madrid.org. In order to access, requesters will need to sign a data access agreement.

Data will be available 3 months to 5 years after publication of the article.

Researchers submitting a methodologically sound proposal should contact miguel.saenz@salud.madrid.org. In order to access, requesters will need to sign a data access agreement.