Can pregnancy cause a moderate increase in red blood cells on a urinalysis?

Yes, Pregnancy Can Cause Moderate RBCs on Urinalysis

Microscopic hematuria is common during pregnancy, occurring in approximately 20% of pregnant women, and is generally a benign physiological finding that does not require extensive workup or impact pregnancy outcomes 1, 2.

Why This Occurs

Pregnancy induces significant physiological changes in the urinary tract that can lead to increased red blood cell excretion:

• Normal pregnancy reference intervals for RBC excretion are up to 23/µL or ≤2,500 RBCs/mL in concentrated early-morning urine samples 3, 4
• These values are higher than non-pregnant women, reflecting pregnancy-specific alterations in renal blood flow, glomerular filtration, and tubular function 3
• The concentration of RBCs actually decreases as pregnancy progresses, with significantly lower levels in the third trimester compared to the first trimester 4

Clinical Significance

The key point is that microscopic hematuria in pregnancy rarely signifies underlying pathology:

• The rate of malignancy in pregnant women with microhematuria is extremely low 1
• Studies show no significant difference in pregnancy complications (preeclampsia, preterm delivery, or small-for-gestational-age babies) between women with and without hematuria 5, 2
• When 66 pregnant women with confirmed microscopic hematuria underwent full evaluation, renal imaging was normal in all but one, and all had normal kidney function 2

Recommended Approach

For asymptomatic microscopic hematuria in pregnancy:

1. First, exclude benign causes - gynecologic bleeding (use vaginal tampon during collection), urinary tract infection, and other obvious sources 1

2. If hematuria persists after excluding infection and contamination:

   • Ultrasound of kidneys and bladder is the appropriate initial imaging modality during pregnancy 1
   • Defer comprehensive workup until after delivery unless concerning features develop 1

3. Postpartum follow-up is recommended - approximately 50% of women with pregnancy-related hematuria will have persistent hematuria at 3 months postpartum, suggesting underlying mild glomerulonephritis that warrants evaluation 2

Important Caveats

• Do not pursue aggressive imaging during pregnancy - CT and MRI with contrast are not indicated for isolated asymptomatic microhematuria 1
• Distinguish from proteinuria - while hematuria is common and benign, new-onset proteinuria with hypertension requires different management for preeclampsia evaluation
• Symptomatic hematuria (gross hematuria, pain, infection symptoms) requires different evaluation than asymptomatic microscopic findings