Ultimately the most morbid sequelae that can result from obstructive uropathy are defects in lung maturation and renal maldevelopment. Clear indications for sonography include discrepancies in fundal height for gestational age, elevated levels of maternal serum alpha fetal protein, and a history of previous pregnancies resulting in congenital anomalies. Regardless of the controversy, when a gestational ultrasound is performed certain basic details must be covered in the examination. By the 20th week of gestation, the internal architecture of the kidneys can be assessed. A normal fetal ureter is rarely visualized during ultrasonography.
Hydronephrosis is the most common abnormality detected on prenatal ultrasonography.
When prenatal hydronephrosis is discovered on ultrasound, the finding does not confirm the presence of obstruction. This is due to the extremely elastic nature of the fetal kidney. This finding is characterized by varying degrees of renal pelvic dilation. The most common cause of UPJ obstruction is an intrinsic narrowing of the proximal ureter. This narrowing can be likened to a scar or stricture in the ureter as it leaves the kidney.