Ultrasound Measurement of Foetal Kidney Length during Healthy Pregnancy: Relationship with Gestational Age

BACKGROUND: Foetal kidney length (FKL) measurements and comparisons to normal charts can be used to assess the development of the foetal kidneys throughout the entire course of pregnancy. This study was designed to assess FKL between 20 — 40 weeks' gestation, establish reference ranges for FKL and determine the relationship between FKL and gestational age (GA) in normal pregnancy. METHODS: This descriptive, cross-sectional study was conducted between March-August 2022, at the Obstetric Units and Radiology Departments of the two tertiary health facilities, one secondary facility and one radio-diagnostic facility in Bayelsa State, Southern Nigeria. Transabdominal ultrasound scan was used to evaluate the foetal kidneys. The relationship between foetal kidney dimensions and GA was explored using Pearson's correlation analysis. Linear regression analysis was done to define the relationship between GA and mean kidney length (MKL). A nomogram predicting GA from MKL was constructed. Level of significance was set at p<0.05. RESULTS: There was a very strong significant correlation between foetal renal dimensions and GA. The correlation coefficient between GA and mean FKL, width and anteroposterior diameter were 0.89 (p=0.001), 0.87 (p=0.001) and 0.82 (p=0.001), respectively. A unit change in mean FKL corresponded to a 79% change in GA (ɼ2), showing a very strong association between mean FKL and GA. The regression equation: GA = 9.87 + 5.91 x MKL, was derived for estimation of GA for a given MKL. CONCLUSIONS: Our study revealed a significant relationship between FKL and GA. The FKL can therefore be reliably used to estimate GA.