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.