Fetal Kidney Length as a Parameter for Determining Gestational Age From the 20th Week in Healthy Women With Uncomplicated Pregnancy

Background: For the best obstetric care, gestational age (GA) must be accurately estimated. However, as biological variability increases in the second and third trimesters, the accuracy of traditional biometric markers decreases. In this regard, fetal kidney length (FKL) has become a viable substitute due to its steady linear growth and its independence from growth disorders. The purpose of this study was to determine the function of FKL in determining GA beyond 20 weeks and to examine its association with recognised fetal biometric parameters. Aim: The study aims to evaluate FKL as a parameter for determining GA from 20th weeks onwards in healthy women with uncomplicated pregnancy. Methods: In this prospective cross-sectional study, conducted between April 2023 and March 2024, at the department of radio-diagnosis at a tertiary care facility, 203 pregnant women with clear-cut singleton pregnancies longer than 20 weeks of gestation participated. Using the most recent menstrual cycle and, if available, an early ultrasound, GA was calculated. Bi-parietal diameter, head circumference, abdominal circumference, femur length, and FKL were all measured using ultrasonography. Relationships between FKL GA and other biometric markers were evaluated using Pearson's correlation coefficient. Results: GA and FKL showed a significant positive connection (r = 0.953, p < 0.001). FKL was also shown to be significantly correlated with head circumference (r = 0.948), femur length (r = 0.887), biparietal diameter (r = 0.949), and abdomen circumference (r = 0.954). According to regression analysis, a 1 mm increase in FKL was associated with a GA increase of almost 0.9 weeks. Conclusion: FKL can be used as a useful supplement to regular fetal biometry and is a dependable and repeatable measure for determining GA after 20 weeks. Clinical implications: The accuracy of gestational dates can be increased by including FKL into regular ultrasonography, especially in late-presenting foetuses with unclear menstrual histories.