Accuracy of foot-length in determining gestational age and birth weight of newborns at Moi Teaching and Referral Hospital

Abstract

Background: Prematurity is a leading cause of neonatal morbidity and mortality. Early and accurate identification of newborns at risk and the institution of community-level interventions could reduce morbidity and mortality. Foot length measurement can be an essential tool to quickly assess and refer those requiring specialized care. However, there is a paucity of data assessing its accuracy in Kenya, especially at Moi Teaching and Referral Hospital (MTRH) Objective: To determine the accuracy of foot length in determining the gestational age and birth weight of a newborn and to identify an operational cut-off foot length for preterm and low birth weight babies born at MTRH Methods: A hospital-based cross-sectional study was conducted at the Riley Mother and Baby unit of MTRH. All babies born between 16th June 2021 and 30th June 2022 whose mothers had an obstetric ultrasound done between 6 to 23 weeks gestation had their foot length measured. A consecutive sampling method was used to select subjects. Ultrasound was used as the gold standard for determining gestational age. Foot length was measured within 24 hours of delivery using a digital vernier caliper and a hard plastic ruler. Birth weight was measured using a digital salter scale. Data was imported into STATA/MP Version 13, coded, cleaned, and analyzed. Receiver operating characteristic curves were used to identify optimal cut-off points for feet measurements that identify preterm and low birth weight neonates. Sensitivity, specificity, positive and negative predictive values were calculated for different cut-off points. The area under the curve (AUC) was used to describe the overall accuracy of foot length in diagnosing premature and low birth weight; A value of 0 was interpreted as perfectly inaccurate, while a value of 1 reflected a perfectly accurate foot length measurement in the ROC curve. Results: A total of 414 neonates were recruited into the study. The males were 221(53.4%). 59(14.3%) were premature (<37 weeks) as determined by ultrasound. 59 (14. 3%) had a birth weight of less than 2500 grams with a mean of 3019 ± 625 grams. There were 10(2.4), 7(1.7%), and 397(95.8%) classified as Small, Large, and Appropriate for gestational age, respectively. The foot length cut off for identifying premature neonates by Vernier Calliper and the plastic ruler was 7.4 cm with a sensitivity of 83% and specificity of 86%. The area under the receiver operating characteristics curve (AUC) at cut-off by the vernier calliper was 0.9 with a positive and negative predictive value of 96.9% and 45.3%, respectively, while the AUC by the plastic ruler was 0.89 with a positive and negative predictive value of 96.3%and 44.7% respectively. Conclusions: The operational cut-off foot length to identify preterm babies is 7.4 cm using a plastic ruler and digital vernier Calliper. The accuracy of foot length was good, depicted by a high sensitivity and specificity. Recommendations: Foot length measurement by a plastic ruler or vernier Caliper can be used in resource-constrained regions to quickly assess the gestational age of a newborn and institute appropriate management.