Kidney malfunction

  I am a 35 year old female, currently pregnant (22 weeks) and after observing recurrent traces of protein in the urine I asked the radiologist to take a look at my kidneys following a fetal scan I was having.
  He observed and enlarged kidney which looked like a "plastic bag" - thin walls and the shape was like a lotus leaf rather than a proper kidney shape. My other kidney looked fine (In fact it looked large and he said it may suggest it has been compensating for some time). He let me drink some water and looked at the bladder. The 'injection' of urine into the bladder could only be noticed from the side of the "good kidney". His observation was that my ureter was obstructed and that he assumes that was the problem.
  I had a reflux operation at the age of 6. I was followed up until the age of 12 with no recurring problems. I had ultrasound scans of the kidneys at age 19 and 26 and they seemed fine.
  Since I had two c-sections in previous deliveries the radiologist suggested that possibly during my operation either the gynecologist sewed my ureter or a blood clot could have blocked it resulting in its obstruction leading to the kidney damage.
  In a blood test I recently took the creatinine level was 0.9 mg/dl (normal range 0.6-1.7) and the Albumin 3.2 g/dl (3.0-5.1 normal range).
  I have several questions:
  Does the obstruction theory make sense (and if it does does it make a difference? - that is can it be reversed?)
  Assuming the damage to the kidney has been done, and it is functioning as the doctor suggested at less than 10%, what would be done? (would it be taken out or left alone?)
  Are there any cons to leaving it alone? (I have not experienced any infections in the past 10 years)
  I understand that accurate kidney function tests require radioactive ingredients and x-ray exposure which I can not do in pregnancy. How indicative is the ultrasound I did and are further examinations really needed?
  What is the difference between a Nephrologist and a Urologist?
Urinary tract obstruction is not uncommon following ob/gyn surgical procedures.  Usually a ureter (the connection from the kidney to the bladder) is accidentally tied off in the pelvis.  This can be surgically corrected.  When this occurs, the opposite kidney will compensate for this, considering it is healthy.
As for your description of your ultrasound, your kidney may show signs of being hydronephrotic (dilated), but it may not be due to obstruction.  You stated that you had surgery for vesicoureteral reflux in the past.  Reflux alone can cause a kidney to look dilated without an anatomical obstruction.  However, surgical repair of reflux has good results (>95% cure).  
The study that may determine if obstruction is present is a lasix renogram.  It can also tell how much function is present in each kidney.  
Assuming that you have decreased function in the "dilated" kidney, and there is evidence of obstruction, there is a chance that the kidney may recover some of the function after the obstruction is surgically corrected.  The surgical procedure would depend on where the level of obstruction is located.  Follow-up studies would then be indicated to see if the kidney recovers function.
It is controversial how to manage this problem.  You have no problems now.  Some elect to have the kidney removed if it has poor function without a chance of recovery.  This would spare you an additional operation.  But, given your age, you could elect to try and salvage the kidney.  
Some patients develop problems with pain, blood in the urine, and hypertension.  It is hard to prove, however, that the kidney is responsible for the high blood pressure.  The incidence of hypertensive due to unilateral renal obstruction is low.
At any rate, because you are asymptomatic, you may discuss deferring a workup of the kidney until after your pregnancy.  Physiologic changes of pregnancy is another reason for "dilated" kidneys.
Lastly, a nephrologist is a medical doctor.   He treats medical diseases of the kidneys (glomerulopathies, diabetes, SLE, hypertension, etc.).  A urologist is a surgical physician.  He/she treats anatomical disease of the kidneys (cancer, obstruction, cancer, erectile dysfunction) in addition to some medical disease of the kidney, ureter, bladder and reproductive system.
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