Objective To determine whether purposely designed nutritional guidelines for extremely low birthweight (ELBW; birth weight <1000 g) babies result in protein intakes that meet international consensus recommendations, and whether this results in improved growth from birth to discharge.

Design A prospective cohort study of nutritional intakes and growth in ELBW babies.

Setting A tertiary neonatal intensive care unit in New Zealand.

Patients 100 ELBW babies who survived for the first month of life, 50 before the introduction of the guideline (Lo Pro) and 50 after (Hi Pro).

Intervention Introduction of a nutritional guideline aimed at increasing protein intakes to meet international consensus recommendations.

Main outcome measures Weekly protein intakes over the first month of life and growth until discharge.

Results Hi Pro babies had significantly higher protein intakes in the first month of life than Lo Pro babies (mean (SD), 3.8 (0.3) vs 3.3 (0.4) g/kg.day, p<0.0001) and a significantly greater growth velocity (GV) over the first 30 days after regaining birth weight (19.5 (5.0) vs 16.2 (5.4) g/kg.day, p<0.002). Hi Pro babies had a significantly lesser Z-score change between birth and discharge than Lo Pro babies for weight (0.0 (1.2) vs −0.9 (1.1), p=0.001), length (−0.8 (0.8) vs −1.2 (1.1), p=0.02) and head circumference (−0.2 (1.1) vs −1.1 (1.6), p<0.001).

Conclusions Simple, standardised nutritional guidelines can result in recommended protein intakes for ELBW babies being achieved and result in increased GV. Downward crossing of centiles between birth and discharge, common in ELBW babies, is significantly reduced for weight, length and head circumference.