Determination of gestational age by ultrasonographic measurement of fetal kidney length during third trimester of pregnancy

Abstract

Objective The aim of accurate estimation of gestational age is reduction of fetal and maternal morbidity and mortality as much as possible. The routine fetal biometry ultrasound (US) measurement at third trimester is not adequate all times; for this purpose, new parameters must be developed. Average fetal kidney length (FKL) is one of them and may add value as a single parameter. Design A prospective study to assess the gestational age at the third trimester using FKL US measurement was done. Patients and methods Seventy-five noncomplicated pregnant women at third trimester (25 as a training sample and 50 as a validating sample) were included in the study. All of them had accurate date of last menstrual period and had regular follow-up at the Department of Obstetrics and Gynecology. Routine US biometry and FKL were done. The training sample was used to calculate a regression equation of gestational age by FKL, and then the validation of the regression equation was done on the validating sample. Main outcome measures To compare the results of gestational age by FKL measurement derived from the regression equation to gestational age by sure last menstrual period date to calculate accuracy and standard error of the estimate. Results There is a strong correlation between gestational age by date and estimated average kidney length in the third trimester, using linear regression analysis (Pearson's r = 0.871;P > 0.001). The derived regression equation [gestational age using FKL (days)=51.1165 + 5.02 × average kidney length (mm)] could estimate the actual gestational age with an accuracy of ±6.4 days (SE of the estimate). Conclusion Average FKL can be used as a new single parameter with some degree of confidence for determination of gestational age at the third trimester.