Ultrasound Measurement of Fetal Kidney Length in Normal Pregnancy and Correlation with Gestational Age

Abstract

Background: Belated booking for antenatal care remains a common practice among pregnant women in developing countries. Many of the existing conventional ultrasonographic indices used for assessing gestational age (GA) become increasingly unreliable beyond the 2nd trimester. Materials and Methods: A prospective cross‑sectional study of booked healthy pregnant women with regular menstrual cycles and certain last menstrual period (LMP) were examined using ultrasound over a 6‑month period. Fetal kidney length (FKL) was measured, beginning from 20 to 41 weeks of gestation. Results: A total of 400 pregnant women were examined. The mean left FKL was slightly but significantly higher than the mean right FKL across the various weeks of gestation (P < 0.05). The mean combined FKL (MKL) was 32.18 ± 5.96 mm, with a reference range of 20.87 ± 0.75 mm to 41.41 ± 0.07 mm from 20 to 41 weeks of gestation. There was strongly positive significant correlation between MKL in millimeters and GA by the LMP in weeks (r = 0.997, P = 0.000). The standard error of prediction (SE) of GA was least for MKL (±7.17 days), followed by femur length (FL) (±8.38 days), head circumference (HC) (±9.02 days), abdominal circumference (AC) (±9.14 days), and biparietal diameter (BPD) (±10.36 days). The best multiple regression model for predicting GA included the five variables such as MKL, FL, BPD, HC, and AC, with a SE of prediction of (±6.31 days). Conclusion: FKL can serve as an additional reliable parameter for accurate dating of GA during obstetric scan.

Keywords: Fetal kidney length, gestational age, pregnant women, ultrasound