Postnatal growth is a crucial in premature infants as it could be correlated with the long-term cognitive development. Optimal nutritional care is required to reduce the initial weight loss and further growth deficit.

The quantitative objective is to achieve growth that is at least equivalent to that of the fetus (on average 15 g/kg.day (12-18 g/kg.day according to gestational age). Children often grow during difficult 10-15 first days of life, so they accumulate a delay that should compensate them secondarily. Therefore, optimum postnatal growth is rather 20 g/kg.day than 15 g/kg.day.

Individualized fortification of human milk (HM) has been proposed to optimize postnatal growth. Specifically, the lack of protein intake is responsible for sub-optimal postnatal growth in preterm infants.

The objectives of this study are to determine the effectiveness of additional protein fortification (APF) in terms of short-term growth along with the proportion of extremely low birth weight (ELBW) infants requiring APF.

In a retrospective, single-center study, premature infants weighing <1250 g at birth hospitalized in investigators' neonatal intensive care unit in 2012, who were exclusively fed with fortified HM and received APF for >12 consecutive days were included.

Weight gain (g/kg•d) over the previous 7 days was calculated daily based on weight data in patients' electronic medical records. When weight gain was considered insufficient (i.e., below 20 g/kg•d) and the serum urea level was <3 mmol/L, 1 g/kg•d protein was added. Before using the mixture, investigators verified that the osmolality was only slightly increased (from 412 to 422 mOsm/kg).

Growth and digestive tolerance were compared between the week before (Wk0) and 1 and 2 weeks after (Wk1 and Wk2, respectively) the introduction of protein supplement; each participant served as his own control. Change from baseline for body weight was the main outcome. Energy and protein intake during Wk0, Wk1, and Wk2 were calculated. Standard deviation z-scores for growth parameters were calculated 7 days before, at time of protein introduction, and 7 and 14 days after . Changes in Z-scores were calculated. The digestive tolerance score and metabolic tolerance (serum urea) were assessed during Wk0, Wk1, and Wk2 (5).

Inclusion Criteria:

• infants weighing <1250 g at birth
• exclusively fed with fortified HM

Exclusion Criteria:

- Severe malformations

Premature infants weighing <1250 g at birth, who were exclusively fed with fortified HM and received additional proteinfortification for >12 consecutive days.