Kidney length, a visceral parameter predicts foetal age between 24 to 40 weeks of gestation
Keywords:Foetal kidney length, Gestational age, Ultrasound
Background: Accurate estimation of gestational age is important in providing appropriate antenatal care. Recent evidence suggests that weightage should also be given to kidney length in addition to standard biometric parameters in determining the duration of pregnancy by ultrasound.
Methods: In a single centre, prospective cross-sectional study was done in 120 pregnant women. In addition to standard biometric parameters, kidney length was also measured between 24 to 40 weeks at two-week intervals. A total of 240 renal vertical measurements were done and average of right and left renal lengths was taken as a final kidney length. Descriptive analysis was carried out to find the mean and standard deviations for each variable. Regression analysis was carried for each variable either singly or in combinations and Pearson regression coefficients was used to find the association between gestational age and various foetal parameters and to determine which of the regression model gives the best fit for prediction of gestational age.
Results: Foetal kidney length progressively increased throughout the gestation (from 23.2 mm at 24 weeks to 40.1 mm at 40 weeks). The regression formula using only kidney length as an independent variable (gestational age=2.195±0.942 X kidney length) had high degree of correlation (R2 0.97, p<0.001, SE of prediction 4.7±3.9), which was superior to other prediction models using standard biometric parameters. In multiple regression models using several conventional parameters, when femur length was added in a stepwise manner, there was significant improvement in forecasting gestational age.
Conclusions: Present study showed that foetal kidney length is a reliable indicator of gestational age between 24 to 40 weeks of pregnancy and may be of utility in pregnancies with wrong dates, non-availability of dating scan and women who have conceived during lactational period.
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