Foot Length for Gestational Age Assessment and Identification of High-Risk Infants: A Hospital-Based Cross-Sectional Study

Assessing the diagnostic accuracy of postnatal clinical scoring methods and foot length measurement for estimating gestational age and birthweight of newborns in low- and middle-income countries: a systematic review and meta-analysis

BACKGROUND

This study aimed to update systematic reviews and meta-analyses on the diagnostic accuracy of postnatal clinical scoring (PCS) methods and foot length (FL) measurement for assessing gestational age (GA) and birth weight in low-income and middle-income countries (LMICs). In addition, the quality of reference standards, including antenatal ultrasound (A-US), last menstrual period (LMP), PCS and newborn weighing scales, was also evaluated.

METHODS

Studies from LMICs published between January 2000 and February 2024 were searched, using databases such as PubMed, Web of Science, Cochrane Library, CINAHL and Scopus. Studies that compared PCS and/or FL with LMP and/or A-US to estimate GA or used calibrated newborn weighing scales for birthweight estimation were included. The risk of bias was assessed using the Quality Assessment of Diagnostic Accuracy Studies-II tool and evaluated the quality of the reference standards. When sufficient data were available, pooled estimates were calculated using random-effects models.

RESULTS

A total of 50 studies were included. A-US was a reasonable tool for GA assessment if conducted by physicians using fetal biometry and the Hadlock method for GA estimation. LMP was reasonable when women had regular cycles, knew their LMP, were not using contraceptives and LMP data were collected by healthcare providers. When A-US was used as the reference standard, PCS methods estimated GA with a precision of ±2.8 to ±3.2 weeks. FL measurement <7.5 cm showed a pooled sensitivity of 76.2% and specificity of 36.6% for identifying preterm birth. FL measurement ≤7.6 cm had a pooled sensitivity of 78.6% and specificity of 65.7% for identifying low birth weight (LBW). High heterogeneity across studies was observed.

CONCLUSION

This systematic review and meta-analysis highlights significant variability and methodological inconsistencies in using PCS methods and FL measurement for estimating GA and LBW in LMICs. The observed high heterogeneity across studies suggests a cautious interpretation of the results.

PROSPERO REGISTRATION NUMBER

CRD42020209455.

Diagnostic accuracy of foot length measurement for identification of preterm newborn in rural Sindh, Pakistan

INTRODUCTION

Assessing gestational age accurately is crucial for saving preterm newborns. In low and middle-income countries, such as Pakistan, where access to antenatal ultrasonography (A-USG) is limited, alternative methods are needed. This study evaluated the diagnostic accuracy of foot length (FL) measurement for identifying preterm newborns in rural Pakistan using A-USG as the reference standard.

METHODS

A test validation study was conducted between January and June 2023 in rural Sindh, Pakistan, within the catchment area of the Global Network for Maternal Newborn Health Registry, Thatta. Singleton newborns whose mothers had an A-USG before 20 weeks of gestation were enrolled. A research assistant measured FL three times using a rigid transparent plastic ruler within 48 hours of birth and the average FL was reported. Sensitivity, specificity, positive and negative predictive values (PPV, NPV) and likelihood ratios were calculated. The optimal FL cut-off for the identification of preterm newborns was determined using the Youden Index.

RESULTS

A total of 336 newborns were included in the final analysis, of whom 75 (22.3%) were born before 37 weeks of gestation. The median gestational age of the newborns was 38.2 weeks, and the median FL was 7.9 cm. The area under the curve was 97.6%. The optimal FL cut-off for identifying preterm newborns was considered as ≤7.6 cm with a sensitivity of 90.8%, specificity of 96.0%, PPV of 86.7% and NPV of 97.3%. A lower cut-off of ≤7.5 cm had a sensitivity of 95.4%, specificity of 84.0%, PPV of 63.1% and NPV of 98.5%.

CONCLUSION

In conclusion, this study highlights the utility of FL measurement for identifying preterm newborns in rural settings where A-USG is unavailable before 20 weeks of gestation. Optimal cut-offs of ≤7.6 and ≤7.5 cm provide a simple, cost-effective and reliable tool for clinicians and frontline healthcare providers in rural areas, respectively.

TRIAL REGISTRATION NUMBER

NCT05515211.