The neorule: a new instrument to measure linear growth in preterm infants.

Objectives: To compare measurements of crown-heel length (CHL) made with the neorule with CHL measurements made with a stadiometer in term infants. To examine safety and reproducibility of CHL measurements in infants < 32 weeks gestational age (GA) using the neorule.

Methods: Three measurements of CHL were made by three teams during the first 2 days of life in healthy term infants. One team used the stadiometer and two the neorule. Two different teams made three measurements of CHL on four occasions at two week intervals in infants less than 32 weeks GA. Infants were continuously monitored, and any adverse event was recorded.

Results: Fifty term infants were studied, median (range) birth weight 3440 (2020-5010) g. The mean (SD, 95% confidence interval) difference between values obtained with the stadiometer and neorule was 0.08 (6.22, -1.69 to +1.85) mm and between the two neorule teams was 0.8 (4.48, -0.47 to +2.08) mm. Twenty preterm infants were studied, GA median (range) 29 (25(+0)-31(+6)) weeks, median (range) CHL 397 (339-475) mm. There were no adverse events. The difference (SD, 95%CI) between teams in the mean CHL measurement was 0.18 (4.79, -1.02 to +1.38) mm, with interobserver limit of agreement -9.2 to +9.6 mm and coefficient of variation 1.2%. There were no significant differences between measurements made by single observers; the F ratio was 0.449 (df = 61, p = 0.6).

Conclusion: The neorule is a safe and accurate way to measure CHL in newborn infants.