What are the possible causes of hematuria in a pregnant woman during the first trimester?

Causes of Hematuria in the First Trimester of Pregnancy

Hematuria in the first trimester is most commonly caused by urinary tract infection, physiologic hydronephrosis with ureteral compression, subchorionic hematoma, or contamination from gynecologic bleeding, with ultrasound of the kidneys and bladder being the only appropriate initial imaging after excluding these benign causes. 1, 2

Primary Etiologies to Consider

Benign Pregnancy-Related Causes

• Urinary tract infection is the most common pathologic cause and should be excluded first with urinalysis and urine culture 1, 2
• Physiologic hydronephrosis develops during the second trimester but can begin in late first trimester, caused by ureteral compression between the pregnant uterus and pelvic brim, occurring in over 80% of pregnancies and more pronounced on the right side 3
• Subchorionic hematoma occurs in 7-27% of pregnancies and can present with vaginal bleeding that may be mistaken for hematuria; transvaginal ultrasound is the primary diagnostic modality 4
• Gynecologic bleeding from the cervix or vagina can contaminate urine samples and must be distinguished from true hematuria 1, 2

Non-Pregnancy-Specific Causes

• Asymptomatic microscopic hematuria occurs in approximately 20% of pregnant women, similar to non-pregnant women, and is often benign 2, 5
• Urolithiasis remains a consideration in pregnancy 6, 7
• Benign causes such as mild glomerulonephritis may be present but rarely impact pregnancy outcome 5

Diagnostic Approach

Initial Evaluation

• Begin with thorough history focusing on dysuria, fever, flank pain, and timing of bleeding relative to urination, plus physical examination to distinguish urinary from gynecologic sources 1, 2
• Perform complete urinalysis with microscopic examination to confirm true hematuria and assess for infection, casts, or proteinuria 2
• Obtain quantitative beta-hCG, complete blood count, and blood type/screen if subchorionic hematoma is suspected 4

Imaging Strategy

• Ultrasound of kidneys and bladder is the only appropriate first-line imaging because it avoids fetal radiation exposure and can identify most structural abnormalities 1, 2
• Avoid CT abdomen/pelvis and CT urography due to fetal radiation exposure 1, 2
• Avoid MRI with gadolinium contrast due to uncertain fetal effects 1, 2
• Defer comprehensive urologic workup until after delivery (at 3 months postpartum) if benign causes are excluded and the patient is asymptomatic 1

Critical Pitfalls to Avoid

Preeclampsia Screening

• If hematuria occurs with hypertension ≥140/90 mmHg or proteinuria >300 mg/24h, screen for preeclampsia as this represents a potential hypertensive emergency requiring hospitalization 1
• This is particularly important if symptoms develop after 20 weeks gestation, though preeclampsia can rarely present earlier 8

Rh-Negative Patients

• Administer anti-D immunoglobulin (50 μg) to Rh-negative patients with vaginal bleeding to prevent alloimmunization, even if the source is uncertain 4

Risk Assessment

• The risk of malignancy in pregnant women with hematuria is low, and aggressive workup with radiation-based imaging is not justified in the first trimester 2
• Microscopic hematuria confirmed on multiple occasions rarely signifies a disorder impacting pregnancy outcome, though postpartum follow-up is recommended to detect persistent hematuria suggesting underlying glomerulonephritis 5

Management Based on Findings

• If UTI is confirmed: Treat with pregnancy-safe antibiotics
• If physiologic hydronephrosis is identified: Reassure patient this is normal; position changes (lateral decubitus on less-affected side or knee-elbow position) can reduce symptoms 3
• If subchorionic hematoma is documented: Prognosis is better when fetal cardiac activity is present; document using M-mode ultrasound rather than pulsed Doppler in first trimester to avoid potential bioeffects 4
• If no benign cause is found and patient is asymptomatic: Arrange postpartum follow-up at 3 months for comprehensive urologic evaluation 1