Detection and assessment of pyelectasis in the fetus: Relationship to postnatal renal function

Objective: To assess the relationship between fetal pyelectasis determined by ultrasonography and postnatal renal function. Methods: We first established normal values for anteroposterior, transverse, and longitudinal diameters of the renal pelvis sonographically in 68 normal fetuses at 30-40 weeks' gestation. We also evaluated prospectively the relationship between the severity of pyelectasis (diameter at least two standard deviations above the normal mean) in 36 fetuses at 30-40 weeks' gestation and postnatal renal function. Fetal renal function also was evaluated through measurement of the hourly urine production rate, whereas postnatal renal function was assessed by technetium 99m-diethylenetriamine penta-acetic acid renography and excretory urography. Results: Fetal pyelectasis was diagnosed when renal pelvic diameters were at least 8 mm (anteroposterior), 11 mm (transverse), and 14 mm (longitudinal), all upper limits of normal diameters of 68 normal fetuses as determined in the first part of the study. Pyelectasis was associated with a normal urine production rate in all fetuses, but in six fetuses it was associated with a normal urine production rate in all fetuses, but in six fetuses it was associated with a progressive deterioration of renal function within the Ist month of life, requiring neonatal surgery. In the other 30 fetuses with pyelectasis, who did not require neonatal surgery, pyelectasis decreased gradually or totally disappeared within 2 years. Renal pelvic anteroposterior, transverse, and longitudinal pelvic diameters were at least 20, 25, and 26 mm, respectively, during late fetal life in those neonates at the time of corrective surgery. The mean anteroposterior diameter in those fetuses who did not require surgery at infancy (11 +/- 6 mm) was significantly less than in those requiring surgery (33 +/- 14 mm, P < .01). Likewise, the transverse diameters were 17 +/- 10 mm and 38 +/- 16 mm (P <.01) and the longitudinal diameters were 20 +/- 10 mm and 48 +/- 22 mm (P <.01). Conclusion: Neonatal surgery is recommended when the anteroposterior, transverse, and longitudinal renal pelvic diameters during the prenatal period are at least 20, 25, and 26 mm, respectively. Surgery is not necessary when the diameters are less than 20 mm. (Obstet Gynecol 1998;92:226-31. (C) 1998 by The American College of Obstetricians and Gynecologists.)