Knee-heel length measurement in healthy preterm infants

Aim-To examine the reproducibility of crown-heel length measurement; the pr ecision and reproducibility of knee-heel length measurement; and the associ ation between the two in healthy preterm infants. Methods-Paired crown-heel and knee-heel lengths were measured on 172 occasi ons by three observers in 43 preterm infants between 205 and 458 days of po stconceptional 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 C V 1.77%, intra-observer CV 2.11%), especially in larger infants. The associ ation 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 infant s, and a poor predictor of CHL.