# Evaluation of Fetal Kidney Measurement as an Adjunct Parameter for Gestational Age Estimation in the Second and Third Trimesters: A Cross-Sectional Study

## TL;DR

This study shows that measuring fetal kidney length can help estimate gestational age in the second and third trimesters when traditional methods are less accurate.

## Contribution

The study introduces fetal kidney length as a new, reliable biometric parameter for gestational age estimation in late pregnancy.

## Key findings

- Fetal kidney length strongly correlates with gestational age (r = 0.844 and r = 0.805).
- Kidney length measurements increase significantly with advancing gestation until 36 weeks.
- Fetal kidney length is a reliable adjunct when traditional ultrasound parameters are inconclusive.

## Abstract

Introduction

Accurate estimation of gestational age (GA) is crucial for effective prenatal management. Conventional ultrasonographic parameters such as biparietal diameter, head circumference, abdominal circumference, and femur length lose precision in late gestation. This study evaluates fetal kidney length (FKL) as an adjunctive biometric tool for estimating GA during the second and third trimesters. The objective of this study was to assess the correlation between FKL and GA.

Materials and methods

A prospective observational study was conducted at a tertiary care center from April 2023 to April 2025, involving 300 singleton pregnancies between 20 and 40 weeks of gestation. Participants with a reliable last menstrual period (LMP) and dating scans were included. Exclusions applied to pregnancies with renal anomalies or systemic complications. FKL was measured via ultrasound in sagittal or coronal planes, and the average of both kidneys was analyzed. GA estimation based on FKL was compared with the American College of Obstetricians and Gynecologists (ACOG) reference standard and Hadlock’s formula using Pearson correlation and t-tests.

Results

Mean right and left kidney lengths were 36.27 mm and 35.26 mm, respectively, showing a strong positive correlation with GA (r = 0.844 and r = 0.805, p < 0.01). FKL measurements significantly increased with advancing gestation until 36 weeks (p < 0.0001).

Conclusion

FKL shows a strong correlation with GA and serves as a reliable adjunct in estimating gestational age in later trimesters, especially when traditional parameters are inconclusive.