Context: CNP plays an essential role in endochondral bone growth. Insight to CNP's paracrine actions is possible using plasma measurements of the amino-terminal fragment of proCNP (NTproCNP). Whether correlations of NTproCNP with linear growth, as found in children and lambs, apply in neonates is unknown.

Objectives: To determine the effects of prematurity, gender and antenatal steroids on plasma NTproCNP at birth, and serial changes in hormone concentrations, linear growth and markers of bone turnover in the first month of post natal life.

Design and setting: Prospective study of newborn infants admitted to an intensive care unit.

Subjects: 48 infants (4 gestation groups) were enrolled. Umbilical cord samples were also obtained from 39 healthy term-infants

Main outcome measures: Plasma NTproCNP and CNP were measured in cord plasma. In enrolled neonates, serial measurements of hormone concentrations and markers of bone turnover were related to tibial growth velocity as measured by knemometry.

Results: Cord plasma NTproCNP was inversely related to gestational age (r=-0.35, p=0.003) and was higher in males (p<0.001). Plasma NTproCNP (p=0.016) and CNP (p<0.001) rose within the first week of life, the increase relating inversely to gestational age (r=-0.64, p<0.001). Plasma NTproCNP at one week was strongly correlated with linear growth velocity (r=0.49, p<0.001), and also at 2, 3 and 4 weeks, the relation being stronger than observed between bone turnover markers and growth velocity.

Conclusions: In neonates with diverse disorders affecting growth and nutrition, plasma NTproCNP was strongly correlated with linear growth during the first four weeks of post natal life, and may prove to be a novel marker of growth plate activity in neonates.