A.  Mild hydronephrosis (or the swelling of the urinary tract part called renal pelvis area) in a fetus at 3rd trimester as in your cousin's case is usually transient and physiologically normal finding. It doesn't have any deleterious effect on the development of the baby. However, it is advisable to closely monitor the size of the hydronephrosis as well as the amount of amniotic fluid through the duration of the pregnancy. This is due to increased risk for fetal kidney injury if the hydronephrosis increases in size.