Rethinking Neonatal Body Proportions: Upper Segment to Lower Segment Ratios in a Rural South Indian Cohort

Introduction The upper segment to lower segment (US:LS) ratio is a key anthropometric measure for assessing body proportions in children, which provides insight into disorders with disproportionate growth. However, body proportions are governed by ethnic, genetic, nutritional, and environmental factors. This study aimed to establish US:LS ratio reference values in live-born neonates from rural Telangana, India; compare US:LS ratios across sex, gestational age categories, birth weight categories, and intrauterine growth status; and assess whether Western normative values apply to this population.  Methods A cross-sectional study was conducted between January and December 2021, at MediCiti Institute of Medical Sciences, Hyderabad, Telangana, India, and 998 neonates were enrolled. Crown-heel length was measured with an infantometer, and the lower segment from pubic symphysis to heel with the help of an inch tape, and the upper segment was derived by subtraction. Neonates were classified by sex, gestational age (preterm, term, post-term), birth weight categories, and intrauterine growth status, and their US:LS ratio was compared. Descriptive statistics included mean and standard deviation for continuous variables and percentages for categorical variables. Independent t-tests were used to compare means between two groups. One-way ANOVA with post-hoc Tukey's honestly significant difference (HSD) was used for comparing more than two groups. A p-value of <0.05 was considered statistically significant. Results The study included 998 neonates, of whom 530 (53.1%) were males, and 468 (46.9%) were females. The mean gestational age ± SD was 38.16 ± 1.29 weeks. The overall mean US:LS ratio was 1.511 ± 0.13. Male neonates exhibited a significantly higher ratio than females (1.519 ± 0.14 vs. 1.502 ± 0.13; p = 0.048). Preterm neonates had a significantly higher mean ratio compared to term infants (1.56 ± 0.15 vs. 1.510 ± 0.13; p = 0.0031). Among gestational age groups, only the comparison between < 32 weeks and 37-39 weeks reached significance (p = 0.0083). Conclusion The mean US:LS ratio of neonates is lower than the typical values available in the literature. There is a gender difference observed with male neonates having a greater US:LS ratio. The mean US:LS ratio differs between preterm and term neonates. There is a need for further large-scale multicentric population-level studies on the US:LS ratio among Indian children. Clinicians should consider population-specific reference values when evaluating neonates for suspected skeletal dysplasia or disproportionate growth.