Variability Over Time of Normal-Sized Fetal Renal Pelvis During the Second Trimester Scan

Area of Science:

• Prenatal imaging
• Fetal medicine
• Medical ultrasonography

Background:

• Accurate fetal measurements are vital for prenatal care.
• The fetal renal pelvis (FRP) size is a key indicator.
• Understanding measurement variability is essential for reliable assessments.

Purpose of the Study:

• To assess the temporal variability of normal-sized fetal renal pelvis (≤5 mm) measurements.
• To evaluate the repeatability of fetal renal pelvis (FRP) anterior-posterior diameter (APD) measurements.
• To analyze intra- and interobserver variations in FRP APD measurements.

Main Methods:

• 98 fetal renal pelvises and 49 fetal urinary bladders were measured at 17-20 weeks gestation.
• Anterior-posterior diameter (APD) of the FRP and bladder diameters were recorded with at least a 30-minute interval.
• Intra- and interobserver variations were analyzed, considering measurement timing and bladder size.

Main Results:

• Fetal renal pelvis (FRP) size variation was ≤1 mm in 85% of cases over time.
• 92% of fetuses maintained an FRP APD ≤4 mm in both measurements.
• Intraclass correlation coefficients (ICCs) indicated moderate agreement for intra- and interobserver measurements.

Conclusions:

• Temporal variation in normal-sized fetal renal pelvis (FRP) anterior-posterior diameter (APD) is minimal.
• Intraobserver variability is the primary contributor to measurement differences.
• These findings support the reliability of FRP measurements within a specific range.