Knee–heel length measurement in healthy preterm infants

AIM To examine the reproducibility of crown–heel length measurement; the precision and reproducibility of knee–heel length measurement; and the association between the two in healthy preterm infants. METHODS Paired crown–heel and knee–heel lengths were measured on 172 occasions by three observers in 43 preterm infants between 205 and 458 days of postconceptional age. RESULTS Crown–heel length (CHL) measurement was highly reproducible, with a coefficient of variation (CV) of 0.41%. Knee–heel length (KHL) measurement was relatively precise (CV 0.78%), but less reproducible (intra-observer CV 1.77%, intra-observer CV 2.11%), especially in larger infants. The association between KHL and CHL was not consistent and varied with age. KHL was a poor predictor of CHL, with a 95% predictive interval of ± 27.5 mm. CONCLUSIONS KHL was less reproducible than CHL, especially in larger infants, and a poor predictor of CHL.