Comparison of Infant Length Measurements Using Tape Measure Versus Length Board

For infants requiring intensive care, infant length is a primary gauge of nutrition and forms the basis for important future treatment decisions. However, existing evidence demonstrates discrepancies in infant length measurements between tape measure and length board.

To compare the accuracy and reliability of infant length measurements using tape measure (standard practice) and length board in a neonatal intensive care unit (NICU) at a public academic medical center.

Using a single-group, quasi-experimental, repeated-measures design, 108 infants (35.58 ± 3.68 weeks, male 59%, 2124.83 ± 881.69 g) admitted to the NICU were prospectively enrolled. Clinical nurses measured infants weekly per unit-based protocol using tape measures. Study team measured length using length boards within 24 hours of tape measurement. Primary outcome was infant length. Length measurements were converted to sex-specific Fenton or WHO growth percentiles. Linear mixed-effects regression, κ coefficient, intraclass correlation coefficient, and positive predictive value were calculated.

The main effect of measurement conditions and time was significant. Predicted length was 0.38 cm lower for length board than for tape measure over time. Weighted κ coefficient and intraclass correlation coefficient indicated good to excellent agreement. More than 37% of infants shifted to a new percentile category based on both measurements. Positive predictive value of length board at time 1 was 63%.

Length board measurements are reliable for accurate classification of an infant's growth curve to influence diagnosis and future plan of care.

Future research warrants replication using a longitudinal design across multiple sites.