What causes pink urine during pregnancy and how is it treated?

Pink Urine During Pregnancy: Causes and Management

Pink urine during pregnancy most commonly indicates hematuria (blood in the urine), which requires immediate evaluation with urinalysis and urine culture to exclude urinary tract infection—the most critical and treatable cause that poses significant risks to both mother and fetus if left untreated.

Primary Differential Diagnosis

Most Common and Urgent Causes

Urinary tract infection (UTI) is the leading pathological cause of pink/bloody urine in pregnancy and must be ruled out first 1, 2. UTIs complicate up to 10% of pregnancies and represent the second most common ailment after anemia 3.

• Asymptomatic bacteriuria occurs in 2-7% of pregnant women and, if untreated, carries a 20-35% risk of progression to pyelonephritis (reduced to 1-4% with treatment) 1, 4
• Acute cystitis presents with dysuria, frequency, urgency, and often visible hematuria 5
• Pyelonephritis may cause flank pain, fever, and systemic symptoms, with serious maternal complications including preterm labor, sepsis, and ARDS 6

Physiological Causes

Normal pregnancy-related changes can cause benign hematuria 7:

• Physiological hydronephrosis after 20 weeks gestation due to uterine compression of the ureters 7
• Increased glomerular filtration and vascular changes
• The incidence of asymptomatic microhematuria in pregnant women is similar to non-pregnant women, with malignancy rates being extremely low 7

Other Pathological Causes

• Urolithiasis (kidney stones): Can cause hematuria and flank pain; occurs in pregnancy and may induce preterm labor 7
• Glomerular disease: May present with proteinuria alongside hematuria 7
• Trauma or instrumentation
• Gynecologic bleeding mistaken for urinary source 7

Immediate Diagnostic Approach

First-Line Testing

Obtain urinalysis with microscopy and urine culture immediately 1, 2:

• Urinalysis can detect red blood cells, white blood cells, bacteria, and protein 7
• Urine culture is essential to identify bacterial pathogens and guide antibiotic therapy 2
• Any quantity of Group B Streptococcus (GBS) bacteriuria requires treatment and intrapartum prophylaxis 7, 2

Imaging Considerations

Ultrasound of kidneys and bladder is the preferred initial imaging modality during pregnancy 7:

• Safe, radiation-free evaluation for hydronephrosis, stones, and structural abnormalities 7
• CT and CTU are contraindicated due to fetal radiation exposure 7
• MRU without contrast may be considered if ultrasound is inconclusive, but full workup can often be deferred until after delivery for benign findings 7

Treatment Algorithm

If UTI is Confirmed

Treat immediately with appropriate antibiotics for 7-14 days 2:

First trimester:

• Nitrofurantoin is first-line 2
• Fosfomycin as alternative 2
• Avoid trimethoprim/trimethoprim-sulfamethoxazole (teratogenic risk) 2
• Avoid fluoroquinolones throughout pregnancy 2

Second trimester:

• Nitrofurantoin remains appropriate 1, 2
• Cephalosporins (cephalexin, cefpodoxime, cefuroxime) are safe alternatives 2
• Beta-lactams (ampicillin) are acceptable 1

Third trimester:

• Avoid nitrofurantoin near term (risk of neonatal hemolysis) 2
• Cephalexin 500 mg four times daily is first-line alternative 2
• Amoxicillin-clavulanate if pathogen susceptible 2
• Fosfomycin (single 3g dose) for uncomplicated lower UTI 2

For pyelonephritis:

• Do NOT use nitrofurantoin (inadequate blood levels) 2
• Cephalosporins for 7-14 days 2
• Initial parenteral therapy may be required for severe cases 2

Critical Follow-Up

Obtain follow-up urine culture 1-2 weeks after completing treatment to confirm cure 1, 2:

• Recurrence is common (up to one-third of patients) 6, 8
• Continue periodic screening with urine cultures throughout remainder of pregnancy after any treated episode 1
• Consider prophylactic antibiotics (cephalexin) for recurrent UTIs 2

If No Infection is Found

If urinalysis and culture are negative and patient is asymptomatic:

• Likely physiological hematuria or gynecologic source 7
• Ultrasound to evaluate for hydronephrosis or stones 7
• Defer comprehensive workup until postpartum if findings are benign 7
• Monitor for development of symptoms

Critical Pitfalls to Avoid

• Never dismiss pink urine as "normal" without urinalysis and culture—untreated bacteriuria increases pyelonephritis risk 20-30 fold 1, 4
• Do not use single-dose antibiotic regimens—they have lower cure rates than 4-7 day courses 1
• Avoid nitrofurantoin for suspected pyelonephritis or near term 2
• Do not skip follow-up cultures—recurrence rates are high and require re-treatment 1, 6
• Remember that asymptomatic bacteriuria MUST be treated in pregnancy (unlike non-pregnant patients) to prevent preterm delivery and low birth weight 1, 4, 3

Maternal and Fetal Outcomes

Treatment of bacteriuria significantly improves outcomes 1:

• Reduces preterm birth from 53 per 1000 to 14 per 1000 1
• Reduces very low birth weight from 137 per 1000 to 88 per 1000 1
• Prevents progression to pyelonephritis with its associated risks of sepsis, preterm labor, and maternal organ dysfunction 4, 5, 6