Tape Rule Measurement of Foot Length as Proxy for Vernier Digital Calliper in Estimating Gestational Age among...

Estimating gestational age at birth could be challenging, particularly in settings where the expertise to use conventional methods is lacking. The use of the postnatal foot length has been proposed for this purpose. The ideal tool for measuring foot length, the Vernier Digital Calliper, is not readily available in resource-poor settings.

To determine the degree of correlation between postnatal foot length measurement using a Vernier Digital Calliper and a tape measure in the estimation of gestational age among Nigerian neonates.

Neonates aged 0 to 48 hours without lower limb deformities were studied. The Gestational age was determined using the New Ballard Scoring method. The Foot length was measured as the distance between the tip of the second toe and the heel using both the Vernier Digital Calliper (FLC) and a non-elastic, flexible tape measure (FLT). The measurements were subjected to statistical comparisons.

A total of 260 newborn infants comprising 140 preterm and 120 term babies were studied. The foot length measurements using both the calliper and tape measure progressively increased with gestational age. FLT was consistently relatively higher than FLC across gestational ages. The relationship between the two tools was FLC = 3.05 + (0.9 x FLT) for preterm babies and FLC = 23.39 + (0.6 x FLT) for term babies. The Cronbach's Alpha correlation ranged from 0.775 to 0.958 across the gestational ages. The degree of agreement between the tools ranged from -2.03 to -1.34 with a mean difference of -1.68 (t = -9.67, p <0.001).

There is a high level of intra-gestational age reliability between caliper measurements and tape measurements, the latter can be suitably used as a suitable proxy for the former in the measurement of postnatal foot length in the estimation of gestational age at birth.