Hydronephrosis of Pregnancy

Hydronephrosis of pregnancy is dilatation of the renal pelvis and ureter during pregnancy, occurring in most women by the third trimester. It results from progesterone relaxation of smooth muscle and compression of the ureters by the enlarged uterus, and is more marked on the right. It matters because it is usually physiological but can mask or cause obstruction, infection and stones.

• Starts at 6 to 10 weeks and peaks at 22 to 26 weeks.
• Resolves within 6 to 12 weeks of delivery.
• Pathological obstruction must be distinguished from physiological dilatation.

Most women have no symptoms. Some have mild loin discomfort, frequency, or recurrent urinary infection; severe pain, fever or haematuria point to obstruction or infection. Examine loin tenderness and temperature.

• Right sided loin ache is common.
• Colic that persists suggests a stone.
• Differential diagnosis: kidney stone, pelvic ureteric junction obstruction, pyelonephritis, ureteric stricture, appendicitis, ovarian vein syndrome, abruption.
• Complications: pyelonephritis, urinary stasis, infected obstruction, stone formation, kidney damage.

The approach is ultrasound with careful interpretation.

• Renal ultrasound: dilated renal pelvis and calyces with a dilated ureter above the pelvic brim; physiological dilatation tapers to the brim.
• Doppler: resistive index above 0.7 or a difference of 0.06 between kidneys, and absent ureteric jet, suggest obstruction.
• Urinalysis with culture, creatinine, electrolytes, full blood count.
• MRI urography without gadolinium for uncertain cases.

The principle is observation for physiological dilatation, and drainage for obstruction with infection or renal impairment.

• Supportive: left lateral position; oral fluids 2 to 3 litres daily; avoid prolonged supine position; monitor symptoms.
• Pharmacological: none for physiological dilatation; paracetamol 1 g oral 6-hourly (maximum 4 g in 24 hours) for discomfort; asymptomatic bacteriuria or cystitis: cefalexin 500 mg oral 6-hourly for 7 days; pyelonephritis: ceftriaxone 1 to 2 g IV 24-hourly until afebrile for 24 to 48 hours, then cefalexin 500 mg oral 6-hourly to complete 10 to 14 days; prophylaxis after infection: cefalexin 250 mg oral at night until 6 weeks postpartum; morphine 2.5 to 5 mg IV for severe pain.
• Procedures: ureteric stent or percutaneous nephrostomy for obstruction with infection, rising creatinine or intractable pain; replaced every 4 to 6 weeks.
• Special groups: women with a single kidney, kidney transplant or previous pelvic ureteric junction surgery have monthly ultrasound and creatinine.
• Red flags: fever above 38 degrees Celsius, severe loin pain, rising creatinine, oliguria, haematuria with clots.
• Follow-up: urine culture monthly; repeat ultrasound at 4 weeks if symptomatic; renal ultrasound at 6 to 12 weeks postpartum to confirm resolution.