# Urologic Considerations in Pregnancy

## Introduction

Pregnancy induces significant physiologic changes in the urinary tract that influence how urologic conditions present, are diagnosed, and managed. The development of physiologic hydronephrosis, increased urinary stasis, and alterations in renal hemodynamics create a distinctive clinical environment. In this context, urologists must carefully balance the health of the mother with the safety of the fetus. A thorough understanding of these physiologic adaptations, the safety profiles of diagnostic and therapeutic interventions, and the management of common urologic emergencies during pregnancy is crucial for urologic trainees.

## Physiologic Changes of the Urinary Tract in Pregnancy

### Renal Changes

During pregnancy, renal plasma flow increases substantially, by approximately 50 to 80% by mid-pregnancy, while the glomerular filtration rate (GFR) rises by 40 to 50%. This enhanced renal function results in a decrease in normal serum creatinine levels, which typically fall to between 0.4 and 0.6 mg/dL; values above 0.8 mg/dL in pregnancy may suggest renal impairment. The kidneys themselves enlarge by 1 to 1.5 cm, a change attributed to increased blood volume and interstitial edema. Additionally, glucosuria can occur physiologically because the filtered glucose load exceeds the tubular reabsorptive capacity during pregnancy.

### Ureteral and Collecting System Changes

Physiologic hydronephrosis is common in pregnancy, occurring in up to 80% of cases. This dilation is more pronounced on the right side, seen in about 80% of affected women, due to the dextrorotation of the uterus, the crossing of the right ovarian vein over the ureter, and the protective effect of the sigmoid colon on the left ureter. Hydronephrosis begins in the first trimester, primarily driven by the hormonal effects of progesterone on smooth muscle relaxation, and progresses in the second and third trimesters as the enlarging uterus mechanically compresses the ureters. The ureteral dilation usually extends to the pelvic brim, where the ureter crosses the iliac vessels. In most cases, this physiologic dilation resolves within four to six weeks after delivery.

### Bladder Changes

The bladder experiences a reduction in capacity as the gravid uterus compresses it, leading to increased urinary frequency, which is a normal physiologic finding during pregnancy. Vesicoureteral reflux may develop or worsen due to changes in the mechanics of the ureterovesical junction. Stress urinary incontinence is also common, particularly in the third trimester.

<image>Anatomical illustration comparing the normal non-pregnant urinary tract with the pregnant urinary tract, showing physiologic right-sided hydronephrosis, the gravid uterus compressing the bladder and displacing the ureters, and the right ovarian vein crossing the ureter, with labeled anatomical landmarks</image>

## Urinary Tract Infections in Pregnancy

### Asymptomatic Bacteriuria

Asymptomatic bacteriuria (ASB) affects between 2 and 10% of pregnant women and must be screened for at the initial prenatal visit, typically with a urine culture performed between 12 and 16 weeks of gestation. Treatment is essential because untreated ASB progresses to pyelonephritis in 20 to 40% of pregnant women. Treating ASB reduces the risks of pyelonephritis, preterm labor, and low birth weight. Safe antibiotic options include nitrofurantoin (which should be avoided after 36 weeks due to the risk of neonatal hemolytic anemia), cephalexin, amoxicillin-clavulanate, and fosfomycin. Fluoroquinolones are contraindicated because of cartilage toxicity, tetracyclines due to adverse effects on teeth and bone, and trimethoprim because of folate antagonism, especially in the first trimester.

### Acute Pyelonephritis

Acute pyelonephritis is the most common serious medical complication during pregnancy, occurring in 1 to 2% of pregnancies, most frequently in the second and third trimesters. It presents with fever, flank pain, costovertebral angle tenderness, and systemic illness. Complications can be severe and include sepsis, acute respiratory distress syndrome (ARDS), preterm labor, and preterm delivery. Management requires hospitalization for intravenous antibiotics—commonly ceftriaxone or a combination of ampicillin and gentamicin—along with intravenous hydration and fetal monitoring. Urine and blood cultures should be obtained before starting antibiotics. Follow-up urine cultures are important, and suppressive antibiotic therapy may be considered for the remainder of the pregnancy to prevent recurrence.

## Urolithiasis in Pregnancy

### Epidemiology and Presentation

Urolithiasis occurs in approximately 1 in 200 to 1,500 pregnancies and is the most common non-obstetric cause of abdominal pain requiring hospitalization during pregnancy. It most frequently presents in the second and third trimesters with symptoms such as flank pain, hematuria, and nausea or vomiting. These symptoms can mimic obstetric complications like placental abruption, preterm labor, or appendicitis. Calcium stones predominate, and pregnancy does not significantly alter the composition of urinary calculi.

### Diagnostic Approach

Renal ultrasound is the first-line imaging modality for suspected urolithiasis in pregnancy, although its sensitivity is limited (34 to 86%) because physiologic hydronephrosis can obscure pathologic obstruction. Transvaginal ultrasound may improve visualization of distal ureteral stones. Color Doppler ultrasound can aid diagnosis by demonstrating the absence of ureteral jets on the affected side, which suggests obstruction; an asymmetry in the resistive index greater than 0.04 between kidneys also supports the diagnosis. Low-dose computed tomography (CT) may be considered in the second or third trimester when ultrasound is non-diagnostic and clinical suspicion remains high. Modern low-dose CT protocols deliver fetal radiation doses below the teratogenic threshold of 50 mGy. Magnetic resonance (MR) urography without gadolinium is a useful alternative that can show hydronephrosis and ureteral dilation, although it cannot directly visualize stones but can identify the level of obstruction. Routine CT in the first trimester, intravenous contrast, and gadolinium are avoided due to their potential fetal risks.

### Management

Conservative management is effective in 70 to 80% of cases and includes hydration, analgesics, and antiemetics. Acetaminophen is the first-line analgesic; nonsteroidal anti-inflammatory drugs (NSAIDs) may be used cautiously and only during the second trimester. Opioids can be administered short-term for severe pain but require monitoring for neonatal respiratory depression if used near delivery. Alpha-blockers such as tamsulosin may be used off-label for medical expulsive therapy, although safety data in pregnancy are limited and risks should be discussed with the patient. Ureteral stenting is indicated for persistent obstruction, infection, intractable pain, or deteriorating renal function; these stents require exchange every four to six weeks due to accelerated encrustation during pregnancy. Percutaneous nephrostomy offers an alternative for decompression, especially in patients with infected hydronephrosis. Ureteroscopy with holmium laser lithotripsy is increasingly used as a definitive treatment and is considered safe when performed without fluoroscopy, ideally in the second trimester. Shockwave lithotripsy (SWL) is absolutely contraindicated during pregnancy because of the risk of fetal injury.

<image>Management algorithm for urolithiasis in pregnancy, starting with clinical suspicion and renal ultrasound, branching into conservative management pathway (pain control, hydration, observation) and interventional pathway (ureteral stent or percutaneous nephrostomy for obstruction with infection, or ureteroscopy for definitive management), with safety considerations and contraindications highlighted at each decision point</image>

## Other Urologic Conditions in Pregnancy

### Renal Masses

Although incidental renal masses discovered during obstetric imaging are rare, their detection is increasing. Angiomyolipomas may grow under the hormonal influence of pregnancy, and the risk of hemorrhage rises when the tumor exceeds 4 cm in size. Renal cell carcinoma is rare in pregnancy, and its management depends on gestational age, tumor size, and staging. Definitive surgery may be postponed until after delivery if the tumor is stable and confined to the organ.

### Urinary Retention

Urinary retention is uncommon but can occur due to incarceration of a retroverted gravid uterus in the first trimester or following delivery as a result of epidural anesthesia or perineal trauma. Postpartum urinary retention has an incidence between 0.05 and 0.5%, with risk factors including epidural anesthesia, instrumental delivery, and prolonged labor. Management typically involves catheterization, with clean intermittent catheterization used if retention persists; most cases resolve within 24 to 48 hours.

### Adrenal Masses and Pheochromocytoma

Pheochromocytoma during pregnancy carries significant maternal and fetal mortality if undiagnosed. It presents with hypertensive crises that may mimic preeclampsia. Diagnosis is made by measuring plasma free metanephrines, and localization is performed with MRI without gadolinium. Alpha-blockade with phenoxybenzamine should be initiated before delivery, and surgical resection is ideally performed in the second trimester.

| Imaging Modality | Safety in Pregnancy | Notes |
|---|---|---|
| Ultrasound (renal) | Safe; first-line | Limited sensitivity for stones (34-86%) |
| MRI without gadolinium | Safe throughout pregnancy | Cannot directly visualize stones; useful for level of obstruction |
| Low-dose CT | Consider in 2nd/3rd trimester if US non-diagnostic | Fetal dose ~8-25 mGy (below 50 mGy threshold) |
| CT with IV contrast | Avoid | Iodinated contrast crosses placenta |
| Gadolinium-enhanced MRI | Avoid | Gadolinium crosses placenta; associated with fetal risk |
| Fluoroscopy | Minimize | Duration-dependent dose; use only when essential |
| Shockwave lithotripsy (SWL) | Absolutely contraindicated | Risk of fetal injury |

| Intervention | Safety | Timing/Notes |
|---|---|---|
| Conservative management (hydration, analgesics) | First-line | Effective in 70-80% of cases |
| Ureteral stent | Safe | Exchange every 4-6 weeks due to encrustation |
| Percutaneous nephrostomy | Safe | Preferred for infected hydronephrosis |
| Ureteroscopy with holmium laser | Safe | Preferred definitive treatment; ideally 2nd trimester; no fluoroscopy |
| SWL | Contraindicated | Absolute contraindication in pregnancy |

## Radiation Safety in Pregnancy

Fetal radiation exposure thresholds are important to consider when imaging pregnant patients. Exposure below 50 mGy is not associated with measurable increases in fetal anomalies or pregnancy loss. Exposure between 50 and 100 mGy carries minimal risk, and clinical judgment should guide imaging decisions. Exposure above 100 mGy increases the risk of malformations, growth restriction, and intellectual disability. A single abdominal or pelvic CT scan typically delivers a fetal dose of approximately 8 to 25 mGy, which is well below the threshold for teratogenicity. Fluoroscopy doses vary depending on duration and positioning and should be minimized whenever possible. Ultrasound and MRI without gadolinium are considered safe throughout pregnancy.

## Key Clinical Pearls

Physiologic hydronephrosis is nearly universal during pregnancy and predominantly affects the right side; it should not be mistaken for pathologic obstruction. Screening and treatment of asymptomatic bacteriuria in all pregnant women are essential to prevent pyelonephritis and obstetric complications. Renal ultrasound remains the first-line imaging modality for suspected urolithiasis in pregnancy, with ureteral jet assessment and resistive index measurements enhancing diagnostic accuracy. Shockwave lithotripsy is absolutely contraindicated during pregnancy, whereas ureteroscopy with holmium laser lithotripsy is the preferred definitive intervention when conservative management fails. Finally, normal serum creatinine levels in pregnancy range from 0.4 to 0.6 mg/dL; values that would be considered normal in non-pregnant patients may indicate renal impairment in pregnant women.

## References

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