eMedicine Specialties > Urology > Stones

Pregnancy and Urolithiasis

Author: Robert O Wayment, MD, Resident Physician, Division of Urology, Southern Illinois University School of Medicine
Coauthor(s): Bradley Fields Schwartz, DO, FACS, Professor of Urology, Director, Center for Laparoscopy and Endourology, Department of Surgery, Southern Illinois University School of Medicine
Contributor Information and Disclosures

Updated: Mar 19, 2009

Introduction

Background

Urolithiasis is the most common cause of nonobstetrical abdominal pain that requires hospitalization among pregnant patients.^1,2 The relative incidence and rate of recurrent calculi in pregnant patients (1 per 1500 pregnant patients) is similar to that in nonpregnant patients.³ Symptomatic stones are found in the ureter twice as often as in the renal pelvis and affect both ureters in equal frequency. Eighty to ninety percent are diagnosed after the first trimester.^4,5

Urolithiasis in pregnancy is often a diagnostic and therapeutic challenge for multiple reasons. First, potential adverse effects of anesthesia, radiation, and surgery often complicate traditional diagnostic and treatment modalities. Second, many signs and symptoms of urolithiasis can be found in a normal pregnancy or may be associated with broad differential diagnoses of other sources of abdominal pathology. Appendicitis, diverticulitis, or placental abruption was mistakenly diagnosed in 28% of patients in a 1992 study by Stothers and Lee.

Finally, most stones (64-84%) pass spontaneously with conservative treatment.^6,7 However, if the calculus does not pass, it may initiate premature labor, produce intractable pain, cause urosepsis in the setting of urinary tract infection, or interfere with the progression of normal labor.

Of the various imaging modalities currently available, renal ultrasonography has become the first-line screening test for urolithiasis in pregnant patients, while limited intravenous pyelography (IVP) or CT scanning is reserved for more complex cases. Ideally, no ionizing radiation should be used in the first or second trimesters, if at all possible. MRI has limited utility in urinary stone disease, and nuclear renography is reserved for functional studies to direct treatment. These are of limited value during pregnancy.

Treatment of stones in pregnancy ranges from conservative management (eg, bed rest, hydration, analgesia) to more invasive measures (eg, stent placement, ureteroscopy with stone manipulation, percutaneous nephrostomy). With appropriate diagnosis and management, the outcome for both the mother and baby is excellent.

Prophylaxis

Prevention is the best cure for urolithiasis, and multiple investigators have suggested prophylactic measures to prevent the difficult course of treating urolithiasis in pregnancy. Denstedt and Razvi (1992) suggested prophylactic treatment of asymptomatic caliceal stones in women of childbearing age who are planning pregnancies.⁸ Biyani and Joyce (2002) recommended metabolic evaluation in known stone formers, as well as prophylactic treatment of asymptomatic stones prior to pregnancy.⁴ In support of their recommendation, they sited Glowacki et al (1992), whose study monitored 107 asymptomatic patients with renal calculi over 31.6 months. They found that 31.8% became symptomatic over that period.⁹

Women with cystinuria who desire pregnancy should seek genetic counseling, and management of their disease should begin prior to pregnancy.¹⁰

Pathophysiology

Although pregnancy-induced urinary stasis and hypercalcemia of pregnancy have been proposed as likely etiologic factors in urolithiasis, this has been disputed. Pregnancy-related events that tend to enhance stone formation include decreased ureteral peristalsis, physiological hydronephrosis, infection, and increased urinary calcium excretion. Augmented excretion of urolithiasis inhibitors, such as citrate, magnesium, and glycosaminoglycans, neutralize these phenomena in pregnant patients, who are no more likely to form urinary calculi than nonpregnant patients.⁸ Coincident to the increased hypercalciuria in pregnancy is an increase in total circulating blood volume, making the relative supersaturation of calcium insignificant.

Anatomic and physiologic changes during pregnancy

Hydroureteronephrosis is the most significant renal alteration during pregnancy. Physiologic dilatation of the collecting system begins in the first trimester at 6-10 weeks' gestation and persists until 4-6 weeks following delivery.⁵ Early theories suggest that hydronephrosis of pregnancy may be a hormonally induced phenomenon whereby ureteral smooth muscles relax in response to high levels of circulating progesterone. In early pregnancy, increased progesterone secretion dilates the ureters and reduces ureteral peristalsis, causing hydronephrosis. Alternatively, the predominant theory ascribes ureteric dilatation to compression of the ureter by the enlarging gravid uterus at the level of the pelvic brim, where the ureter crosses the iliac vessels.

Dilatation is greater on the right side than on the left because of pressure due to physiologic engorgement of the right ovarian vein and dextrorotation of the uterus.⁴ Swanson and associates (1995) observed that hydroureteronephrosis was not routinely found below the pelvic brim and was altogether absent in patients who had undergone urinary diversion.⁵

Volume changes during pregnancy

Glomerular filtration rate (GFR) and renal plasma flow (RPF) increase by as much as 25-50% during pregnancy. Both of these changes are attributable to increases in cardiac output, decreases in renal vascular resistance, and increases in serum levels of progesterone, aldosterone, deoxycorticosterone, placental lactogen, and chorionic gonadotropin. GFR and RPF enhancements also contribute to the increase in glucose, amino acid, protein, and vitamin secretion. As a result of the GFR and RPF modulations, which peak at 9-11 weeks' gestation, renal volume increases during pregnancy by as much as 30% above the reference range. The sustained elevation of prolactin levels in the pregnant patient has a growth hormone–type effect by increasing the glomerular surface area, which also contributes to an increase in renal volume.

Along with increases in GFR and RPF, the filtered load of sodium, calcium, and urate increases. Although calcium and urate excretion increases, sodium excretion remains unchanged. The urinary excretion rate of calcium stone inhibitors, such as citrate and magnesium, also increases in the pregnant patient; likewise, increased glycosaminoglycans and acidic glycoproteins inhibit oxalate stone formation (eg, nephrocalcin). This explains why pregnancy is not associated with a net increase in the rate of stone formation relative to nonpregnant patients. The net effect of these physiologic changes is a stable relative supersaturation of important ions such as calcium oxalate, urate, and phosphate.

Uric acid stone formation

The formation of uric acid stones requires continued and excessive oversaturation of urine with uric acid or extreme aciduria. Dehydration, hyperuricosuria, and significantly acidic urine contribute to uric acid supersaturation and stone formation. However, during gestation, urine tends to be more alkaline, probably because of greater intrinsic purine use and increased urinary citrate excretion. Thus, renal units are generally protected against uric acid stone formation during pregnancy.

Calcium oxalate and calcium phosphate stone formation

Although pathologic calcium oxalate supersaturation has been identified in the urine of pregnant women, the incidence of crystalluria is no higher than in women who are not pregnant. In the pregnant patient, physiologic absorptive hypercalciuria is due to elevated levels of serum 1,25 dihydroxycholecalciferol (1,25 vitamin D). This hormone, which is secreted by the placenta, augments calcium absorption in the GI tract and suppresses parathormone production, increasing renal excretion of calcium. Additionally, dietary supplementation of calcium during gestation further augments calcium excretion. Some reports suggest that calcium excretion increases 200-300% compared with that in healthy patients who are not pregnant. However, increased concentration of the aforementioned urolithiasis inhibitors present in urine during gestation and increased urine fluid output counters the increased risk imposed by any hypercalciuria.

Struvite stones

Struvite stones form only when the urinary tract is infected with urea-splitting organisms (eg, Proteus species). These infected stones are usually composed of pure magnesium ammonium phosphate but may be formed around a coexisting calcium, uric acid, or cystine stone. Struvite stones appear to develop more commonly in the presence of a congenital abnormality of the collecting system.

Frequency

United States

The reported incidence of urinary calculi in pregnant women is around 1 per 1500 pregnant women, which is similar to that in nonpregnant patients.³

Approximately 80-90% of pregnant patients with urinary calculi present with symptoms during the second or third trimester because spontaneous stone passage is more difficult at this stage of pregnancy.

Ureteral stones occur twice as often as kidney stones in pregnant patients.

Approximately 64-84% of renal calculi pass spontaneously with conservative management,^6,7 especially if they 4 mm or smaller. Stones that are 7 mm or larger are much less likely to pass without intervention and often require some type of treatment.

Mortality/Morbidity

Urolithiasis associated with ureteral obstruction and upper urinary tract infection mandates immediate treatment; this is a true urologic emergency that can potentially lead to urosepsis, perinephric abscess formation, or even death in pregnant women. Urolithiasis in a pregnant patient may initiate premature labor or interfere with the progression of normal labor, which poses a significant health risk to the fetus.

Race

Hispanic people and white people are most commonly predisposed to urinary calculi. Black people are less predisposed to kidney stone formation. The exact cause of this discrepancy is not known, but dietary influences may play a role. Calculi in black individuals are more likely to become infected than those in white individuals.

Sex

The reported incidence of urolithiasis is higher in men, with a male-to-female ratio of 3:1, although this ratio is decreasing, possibly because of dietary or obesity trends in the United States.

Age

Urinary stones in women usually manifest during the third to fifth decades of life, with an average age of 24.6 years. Urolithiasis occurs in pregnant women at rates similar to age-matched nonpregnant women.⁵

Clinical

History

Urolithiasis is derived from the Greek words ouron (urine) and lithos (stone). When in the setting of pregnancy, urolithiasis presents as a diagnostic challenge. Clinical manifestations of urolithiasis in pregnant patients often resemble signs and symptoms of pregnant patients without stones, not to mention many other sources of abdominal pathology (see Differentials).

Flank pain (89%) and hematuria (95%) are the most common symptoms of kidney stones⁷ ; however, these findings may also represent physiologic changes of pregnancy. Pregnancy-induced hydronephrosis can cause flank pain and even mimic renal colic,¹¹ and microanatomic alterations in venous fragility of the collecting tubules may cause hematuria.¹² Aside from its presentation in normal conditions, hematuria without discomfort is rare in the presence of a calculus.⁵

Alternatively, pregnant patients with ureteral stones may report pain in atypical locations or the pain of premature labor. Signs of premature labor, ectopic pregnancy, or complicated labor often mimic clinical symptoms of renal-ureteral calculi. Therefore, maintaining a high degree of suspicion in all pregnant women with abdominal or pelvic pain, hematuria (gross or microscopic), or unresolved urinary tract infections is imperative.

• The most common symptoms of urolithiasis of pregnancy include the following:
  • Flank pain
  • Pain radiating to the groin or labia
  • Nausea
  • Dysuria
  • Gross hematuria
• Less-common symptoms of urolithiasis include the following:
  • Lower abdominal pain
  • Fever/chills
  • Vomiting
• Other important historical findings pertinent to urolithiasis include the following:
  • Recurrent or persistent urinary tract infection (especially during the current pregnancy)
  • History of previous calculi, either in a previous pregnancy or in the nonpregnant state
  • Prior urologic surgery
  • History of prior complicated pregnancy or premature delivery
• Sites of urolithiasis may be localized based on the patient's description of pain.
  • Urolithiasis that obstructs at the ureteropelvic junction generally manifests as deep flank pain without radiation to the groin.
  • Urolithiasis within the mid portion of the ureter can cause severe and intermittent pain, pain in the flank, and ipsilateral lower abdomen pain with radiation to the vulvar area.
  • Urolithiasis in the distal ureter or ureterovesical junction may manifest as pain that radiates to the labia and irritative voiding symptoms such as urinary frequency and dysuria.

Physical

• Patients with renal colic are often extremely restless, exhibiting active movement on presentation.
• On inspection, the abdomen may be moderately distended, especially if the patient has coexisting ileus.
• On palpation, the abdomen is soft and tender in the upper quadrant. This differs significantly from the motionless presentation and rigid abdomen of a patient with peritonitis.
• On auscultation, bowel sounds do not provide helpful clues because they may range from hyperactive to markedly diminished because the patient may have concurrent ileus.
• Other signs and symptoms include costovertebral angle tenderness, generalized flank tenderness, and voluntary guarding of the abdominal musculature.

Causes

Stone formation during pregnancy does not appear to have any etiologic factors that are unique to pregnancy. Risk factors associated with urolithiasis in general include the following:

• Heredity
• Age (third to fifth decades of life)
• Decreased water intake
• Increased environmental temperature and/or dry climate
• Diet (eg, high in calcium, sodium, and red meat consumption)
• Occupation (eg, exposure to hot climate)
• Geographic location (eg, southwest United States ["Stone Belt"])
• Social class (related to occupation and diet)
• Excessive weight or obesity (apparently a risk factor in women but not in men)

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• Pregnancy and Reproduction Center
• Pregnancy Overview
• Pregnancy Causes
• Pregnancy Symptoms
• Pregnancy Treatment
• Kidney Stones Overview
• Kidney Stones Causes
• Kidney Stones Symptoms
• Urinary Tract Infections Overview
• Urinary Tract Infection Causes
• Urinary Tract Infections Treatment
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• Intravenous Pyelogram Preparation
• Blood in Urine Treatment
• Kidneys and Urinary System Center
• Blood in Urine Overview
• Causes of Blood in Urine
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• Kidney Stones Treatment
• Urinary Tract Infection Symptoms