Laser-Based Length-Measuring Board for the Measurement of Infant Body Length from Outside an Incubator: Proposal and Assessment of a Model

Introduction: Opening the incubator side wall to insert a non-sterile length-measuring device carries the risk of microbial contamination and thermal instability for preterm infants. To reduce this inconvenience, a laser-based length-measuring board is proposed to measure body length from outside the incubator.

Methods: This device has two laser-line-shaped cursors which can be pointed to opposite ends of a segment to be measured. It is attached to the outer side of one of the incubator's side walls in such a manner as to ensure that its axis is parallel to the longitudinal axis of the segment. To validate the measurements made with this model, a calibrated caliper consisting of a conventional rigid length-measuring board with a resolution of 0.05 mm was constructed to serve as a reference. Crown-heel length was measured in a sample of 45 infants, including 32 preterm and 13 term infants of corrected gestational age at the time of measurement.

Results: Good intra-observer variability was obtained. Near-perfect statistical agreement was found between measurements with both devices, with concordance correlation coefficients of 0.994 (95% CI: 0.990; 0.996) in preterm infants and 0.994 (95% CI: 0.988, 0.998) in infants at term. The clinical relevance of the agreement between measurements was assessed by a Bland-Altman plot, and the difference may reach clinical relevance (up to 1 cm) but without evidence of proportional bias.

Conclusion: The proposed validated laser-based length-measuring board offers a suitable alternative to conventional length-measuring boards for contactless measurement of infant body length.