Role of Ultrasonographic Measurement of Fetal Kidney Length in Determination of Gestational Age during Third Trimester of Pregnancy

Background: In routine ultrasonography, the ultrasonologist measures the bi-parietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL) in estimating the gestational age (GA) and estimated date of delivery. However, as the pregnancy advances these parameters become increasingly unreliable in prediction of GA. Estimation of GA in late second and third trimester accurately still a problem till now. Fetal kidney has been shown a steady growth of 1.7 mm fortnightly (every 2 weeks) along pregnancy and is unaffected by growth abnormalities. Many studies have reported that fetal kidney length (FKL) correlates with the gestational age in late trimester very strong. The study aimed to assess the accuracy of the gestational age estimated by mean fetal kidney length compared to multiple growth parameters like BPD, HC, AC & FL in addition to the actual gestational age derived from the reliable last menstrual period. Methods: Cross sectional hospital based study, was conducted at ultrasound unit;department of Obstetrics and Gynecology, Faculty of Medicine, Ain Shams University from the period of July 2018 to December 2018. A total number of 115 Pregnant women at their third trimester by reliable LMP attended antenatal care clinic at Ain-Shams University Hospital and consented to participate in this study. Every woman was subjected to: Expected date of delivery was calculated according to Naegle’s formula: Ultrasonography: Fetal biometry and estimated date of delivery (EDD) by assessment of BPD, HC, FL & AC. Expected fetal weight measured by Hadlock formula. Fetal lie and presentation. Exclusion of fetal anomalies. Measurement of both right & left fetal kidney length. Results: In this study, 255 participants were recruited and assessed for eligibility, 125 women were allocated to perform obstetric ultrasound just 115 completed and were included in the final analysis. The current study found that there was a highly significant positive correlation between gestational age (according to ultrasound parameters) and KL, BDP, HC, AC and FL but Kidney length was the most correlated parameter. Also this study found that there was significant positive correlation between gestational age (according to LMP) and gestational age estimated by BPD, HC, AC, FL and KL with the most significant positive correlation being with KL. Also this study found that there was no significant difference (matched) in KL and Gestational age compared to other parameters. This means that KL is the most accurate parameter for Estimating Gestational age, correlation between MKL and GA by LMP (r = 0.951, p = 0.000) the most significant correlation. In this study, no significant difference was found between gestational age estimated by KL and gestational age in all stages of pregnancy. This means that KL remains accurate as a predictor for gestational age regardless stage of pregnancy. Conclusion: Kidney length can be used as an individual parameter in estimating gestational age.

Living kidney donor assessment:Kidney length vs differential function

BACKGROUND The key question in living kidney donor assessment is how best to determine the contribution of each kidney to overall renal function and guide selection of which kidney to donate,ensuring safety of procedure and good outcome for both recipient and donor.It is thought that a length difference>2 cm may indicate significant difference in function and therefore need for measurement of differential function.AIM To determine the effect of using kidney length to decide which kidney to donate in a retrospective cohort of potential donors.METHODS All 333 potential living kidney donors between January 2009 and August 2018 who completed assessment were retrospectively evaluated.Donor assessment was performed as per United Kingdom guidelines.Data included age,sex,kidney length(cranio-caudal)obtained by computed tomography/ultrasonography,51-chromium ethylenediamine tetraacetatic acid measured glomerular filtration rate,mercapto acetyl tri glycine split function and vascular anatomy.There were 48 exclusions due to inadequate data or incomplete investigations.Statistical analysis was performed using Excel pivot tables and GraphPad Prism.Correlation between kidney length and differential function was determined with Pearson’s correlation coefficient.RESULTS Of 285 potential donors included in the study,there were 144 males(mean age 49.9±14.75)and 141 females(mean age 51.2±11.23).Overall,the Pearson’s correlation between differences in length and divided function of kidney pairs was 0.1630,P=0.0058.Of 73 with significant difference(>10%)in divided function,18(24.7%)had no difference in kidney length;54(74%)had a difference of<2 cm and only one of>2 cm.Using a length difference of>1 cm would only predict significant difference in divided function in 8/34(23.5%)of cases.Using a difference of>2 cm as cut off for performing split function would lead to false reassurance in 72 patients(6 had>20%difference in divided function whereas 66 had 10%-20%difference).CONCLUSION Length difference between kidney pairs alone is not sufficient to replace measurement of divided function.This issue requires a randomised controlled trial to resolve it.