Objective: To determine reference ranges for normal fetal renal size in a population of pregnant patients at Mayo Clinic Rochester.
Design: Normal fetal kidneys were prospectively analyzed relative to gestational age and to fetal body weight.
Material and methods: In 100 pregnant women, prenatal ultrasound examinations were performed between 18 and 39 weeks of gestation. Fetal renal length and volume were determined by prenatal ultrasonography and compared with gestational age and estimated fetal body weight. Reference ranges as a function of gestational age were obtained for fetal body weight, renal length, renal volume, renal length/ body weight, and renal volume/body weight. Reference ranges as a function of body weight were determined for renal length and renal volume. Polynomial least-squares regression analysis was used to model each of the growth variables (Y) as a function of either gestational age or body weight (X).
Results: Graphic representation of these relationships are presented. These graphs include the 2.5, 5.0, 95.0, and 97.5 percentiles and the predicted value of Y from the regression equations. Fetal body weight, renal length, and renal volume increased throughout gestation, and the ratio between fetal renal volume and body weight remained constant.
Conclusion: These data about normal fetal renal growth relative to gestational age and fetal body weight should help identify fetal abnormalities in renal size or growth patterns.