II. Physiologic alterations in pregnancy.
Pregnancy induces significant physiologic alterations, some of which affect the urinary system.
The most remarkable anatomic change is the dilation of the renal calyces, pelvis, and ureters, which is usually evident by the first 6 to 10 weeks of gestation. Pregnancy-induced hydronephrosis is the most common cause of dilation of the urinary tract in pregnancy and may cause flank discomfort or even mimic renal colic. Upper tract dilation is seen in up to 90% of pregnant women by the third trimester and may persist for as long as 12 weeks post partum.
Other important physiologic changes in pregnancy include an increase in renal plasma flow, which induces a 30% to 50% increase in glomerular filtration rate. As a result of this physiologic alteration, the normal ranges of serum creatinine and blood urea nitrogen are approximately 25% lower for the pregnant patient.The increase in renal plasma flow and glomerular filtration rate also increases the filtered loads of sodium, calcium, and uric acid, causing a state of hypercalciuria and hyperuricosuria.
III. Symtoms and signs.
Renal colic is the most common nonobstetric cause of abdominal pain in hospitalized pregnant women.
The most common presenting symptom is flank pain, usually accompanied by either macroscopic or microscopic hematuria and, in some cases, urinary tract infection.
Other symptoms that may indicate urolithiasis include irritative voiding symptoms, chills, nausea, and vomiting.
IV. Imaging.
1. X-ray.
An important factor in the radiographic evaluation of pregnant patients suffering from stone disease is the risk of ionizing radiation exposure to the fetus. The principal effects of irradiation on the fetus include teratogenesis, carcinogenesis, and mutagenesis.
2. Ultrasonography.
It has become the standard initial study in evaluation of the pregnant patient thought to be experiencing renal colic.
Transvaginal ultrasonography can provide imaging of the distal ureter.
3. CT imaging.
It should be avoided during pregnancy because the radiation dose is particularly high.
V. Treatment.
Approximately 50% to 80% of pregnant patients with symptomatic calculi will pass their stones spontaneously when treated conservatively with hydration and analgesia.
Improvements in ureteroscopic technology and intracorporeal lithotripters have made it possible to access and to treat any stone in the upper urinary tract successfully, even in the pregnant patient.