Hydronephrosis in Pregnancy

I just came across a 24 year old asymptomatic woman with no prior renal issues presenting with acute renal failure at 32 weeks of gestation. Work up was pretty much negative excepting for bilateral hydronephrosis and hydroureters proximally on renal ultrasound. Although hydronephrosis is usually physiologic in pregnancy, we proceeded with ureteral stenting as no other cause of her renal failure is evident. Her urine output improved and renal failure resolved. So I did some literature review on this topic. Here is what I found: Upto 90% of pregnant women show some dilation of the renal pelvis and proximal ureters by the thrid trimester of pregnancy. 2 Reasons: hormonal (progesteron) effect on ureters leading to reduced peristalsis and mechanical effects of enlarging gravid uterus on ureters. The development of hydronephrosis is considered physiologic as it is usually asymptomatic and does not lead to renal failure. Occasionally, you may across a rare patient like our patient with renal failure. The last published case report on this topic that I could find in any nephrology journal is almost 15 years before (Jena et al, AJKD 1996). In this report, authors reported that there were only 18 published case reports of reversible obstructive uropathy linked to the gravid uterus thus far. The risk factors for renal failure are twin gestation, polyhydramnios and solitary kidney but our patient has none of these.