A 29-year-old gravida 2 para 1 presents for a routine prenatal visit at 22 weeks’ gestation. A fetal ultrasound shows unilateral hydronephrosis with dilation of the renal pelvis and calyces. The ureter is not dilated. Amniotic fluid volume is normal. The obstetrician explains that this is the most common site of obstruction in the fetal kidney and that it is related to delayed canalization during renal development. Which of the following is the most likely anatomic level of obstruction in this fetus?