Neonatal length inaccuracies in clinical practice and related percentile discrepancies detected by a simple length-board

Aim: The study aims to assess accuracy of standard practice measurement of neonatal length compared with a gold-standard length-board technique.

Methods: Data were obtained from a population-based, cross-sectional study of 602 term babies at Royal Prince Alfred Hospital, Sydney, Australia, in 2010. Neonatal length was measured by standard clinical practice and by a length-board (gold standard) and measurements compared. Standard growth curve percentiles were used to plot length measurements. The Bland and Altman method was used to assess agreement, and acceptable levels of agreement were set at ≤1 cm and ≤0.5 cm.

Results: The limits of agreement were between -3.06 cm (95% CI -3.08 to -3.04) and 2.67 cm (95% CI 2.65 to 2.69). Neonates whose standard-practice length fell within 0.5 cm of the gold standard totalled 41% (241 neonates), while 59% (342) were >0.5 cm. The change in length resulted in a change in the percentile range of 53% (309) on a standard growth curve percentile. When examining neonates whose length was plotted at the extremes of percentile regions, the positive predictive value results of the standard practice compared with the gold standard were poor, with positive predictive values of 37.5%, 57.1% and 31.3% for neonates who were measured as <3rd, <10th and ≥90th percentile, respectively.

Conclusions: In current clinical practice, measures of neonatal length are often inaccurate, which has implications for potentially erroneous clinical care. Health-care providers should be educated on the importance of length and trained in how to measure length with the correct technique using a length-board.