DETECTION AND ASSESSMENT OF PYELECTASIS IN THE FETUS - RELATIONSHIP TO POSTNATAL RENAL-FUNCTION

Objective: To assess the relationship between fetal pyelectasis determ ined by ultrasonography and postnatal renal function. Methods: We firs t established normal values for anteroposterior, transverse, and longi tudinal diameters of the renal pelvis sonographically in 68 normal fet uses at 30-40 weeks' gestation. We also evaluated prospectively the re lationship between the severity of pyelectasis (diameter at least two standard deviations above the normal mean) in 36 fetuses at 30-40 week s' gestation and postnatal renal function. Fetal renal function also w as evaluated through measurement of the hourly urine production rate, whereas postnatal renal function was assessed by technetium 99m-diethy lenetriamine penta-acetic acid renography and excretory urography. Res ults: Fetal pyelectasis was diagnosed when renal pelvic diameters were at least 8 mm (anteroposterior), 11 mm (transverse), and 14 mm (longi tudinal), 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 fetuse s it was associated with a normal urine production rate in all fetuses , but in six fetuses it was associated with a progressive deterioratio n of renal function within the Ist month of life, requiring neonatal s urgery. In the other 30 fetuses with pyelectasis, who did not require neonatal surgery, pyelectasis decreased gradually or totally disappear ed within 2 years. Renal pelvic anteroposterior, transverse, and longi tudinal pelvic diameters were at least 20, 25, and 26 mm, respectively , during late fetal life in those neonates at the time of corrective s urgery. 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 tran sverse diameters were 17 +/- 10 mm and 38 +/- 16 mm (P <.01) and the l ongitudinal diameters were 20 +/- 10 mm and 48 +/- 22 mm (P <.01). Con clusion: Neonatal surgery is recommended when the anteroposterior, tra nsverse, and longitudinal renal pelvic diameters during the prenatal p eriod are at least 20, 25, and 26 mm, respectively. Surgery is not nec essary when the diameters are less than 20 mm. (Obstet Gynecol 1998;92 :226-31. (C) 1998 by The American College of Obstetricians and Gynecol ogists.)