Peeing Blood When Pregnant: Causes and When to Seek Help

Blood in the urine during pregnancy is surprisingly common, with one study finding that about one in five pregnant women tested positive for microscopic blood on a dipstick test at some point during their pregnancy. The causes range from harmless physical changes in the urinary tract to infections that need prompt treatment. While most cases turn out to be benign, visible blood or blood accompanied by pain, fever, or other symptoms always warrants medical evaluation, because the stakes of missing a treatable condition are higher when you are carrying a pregnancy.

How Common Is It, and Does It Always Mean Something Is Wrong

Many pregnant women are alarmed when a routine urine test comes back with traces of blood, but the finding is often incidental. In a prospective study of over 900 pregnant women, about 20% had dipstick-detected blood in their urine on at least two separate occasions. Among those referred to a kidney specialist for further workup, microscopic blood was confirmed in roughly 60%, yet renal imaging was normal in nearly all of them, and kidney function was fine across the board. The development of preeclampsia, gestational hypertension, or a small-for-gestational-age baby was no different in women with or without the finding.¹

The distinction between microscopic and visible blood matters. Microscopic blood, picked up only on a lab test, is often a side effect of the massive cardiovascular and anatomical shifts your body undergoes during pregnancy. Visible blood, where you can actually see pink, red, or cola-colored urine, is less common and more likely to point to something that needs investigation. That said, even visible blood can have a benign explanation, and microscopic blood occasionally signals something that needs treatment. The point is that context matters more than the blood itself.

Urinary Tract Infections Are the Most Likely Culprit

Urinary tract infections are one of the more common complications of pregnancy, affecting roughly 8% of pregnancies overall. They run a spectrum from silent bacterial colonization, where bacteria are present but cause no symptoms, to full-blown kidney infections. Acute cystitis, the classic bladder infection with burning and frequent urination, occurs in about 1 to 2% of pregnancies. Pyelonephritis, a more serious kidney infection, occurs at a similar rate and is one of the most frequent medical reasons for hospitalization during pregnancy. It peaks in the second trimester.²

Blood in the urine is a recognized symptom of acute cystitis in pregnancy, alongside painful urination, frequent urination, and waking up to pee at night. The reason UTIs are so common in pregnancy comes back to the anatomical changes happening in your body. The growing uterus compresses the bladder and ureters, and hormonal shifts relax the smooth muscle in the urinary tract, making it easier for bacteria to travel upward. Urine that sits in a dilated system rather than draining efficiently gives bacteria more time to multiply.

If a UTI is the cause of blood in your urine, the good news is that treatment is straightforward. Current guidelines recommend starting antibiotics as soon as symptoms and a positive urinalysis point to infection, then adjusting the choice of antibiotic once culture results come back. A typical course runs five to seven days. The preferred options include nitrofurantoin, certain penicillin-type drugs, and fosfomycin, chosen based on what the bacteria are susceptible to and what is safe at your gestational age.² Not all antibiotics are equally safe in pregnancy, however. Penicillins and cephalosporins have the strongest safety profile, while others carry specific risks: tetracyclines can affect fetal bone development, aminoglycosides carry a risk of fetal toxicity, and quinolones are avoided because of concerns about cartilage development.³

Why UTIs in Pregnancy Are Taken Seriously

The urgency around treating urinary infections during pregnancy is not just about resolving your symptoms. Multiple studies have linked UTIs in pregnancy to an increased risk of preterm birth. One large retrospective study found that women with symptomatic lower urinary tract infections had a preterm birth rate of 12%, compared to about 5% in women without infections, putting them at roughly two and a half times the risk even after accounting for other factors.⁴ A separate study found that the elevated risk of preterm birth was especially pronounced in the first week after a UTI diagnosis, suggesting that early detection and treatment could make a meaningful difference.⁵

Even with antibiotic treatment, the risk of preterm birth remains somewhat elevated compared to women who never developed an infection. One study found adjusted risk ratios between 1.1 and 1.4 for births before various gestational thresholds, regardless of whether antibiotics were given.⁶ This does not mean antibiotics are pointless; the risk was slightly higher in untreated women. But it does explain why providers monitor closely even after prescribing treatment, and why repeat urine cultures are standard practice after finishing a course of antibiotics.

Kidney Stones During Pregnancy

Kidney stones are another well-recognized cause of blood in the urine, and pregnancy changes your risk in a clear, time-dependent pattern. In the first trimester, the odds of developing a symptomatic kidney stone are about the same as when you are not pregnant. By the second trimester, the odds roughly double. In the third trimester, they nearly triple. The risk actually peaks in the first three months after delivery, at about three and a half times baseline, before returning to normal by one year postpartum.⁷

The rising risk makes physiological sense. Pregnancy increases the filtration rate of your kidneys and changes the concentration of calcium and other minerals in the urine. At the same time, the ureters dilate under hormonal influence and compress under the weight of the growing uterus, making it harder for small stones to pass on their own. When a stone does become symptomatic, the typical presentation is severe flank pain, blood in the urine, and sometimes nausea. Managing stones during pregnancy is tricky because the imaging tools and surgical options are more limited. Ultrasound is the first-line imaging choice, since CT scans involve radiation. Most stones are managed conservatively with hydration and pain control, though ureteral stents or other procedures may be needed if a stone causes infection or obstructs urine flow.³

Anatomical Changes That Cause Bleeding on Their Own

Pregnancy reshapes your urinary tract in ways that can produce blood in the urine without any infection or stone present. The most common structural change is dilation of the upper urinary tract, which becomes increasingly prominent after about 20 weeks. The collecting system in the kidney and the ureters widen under the combined effect of hormonal relaxation of smooth muscle, direct compression by the enlarging uterus, and shifts in the path of pelvic blood vessels.⁸ This dilation is so common that radiologists consider it a normal finding in the second and third trimesters and will not report it as a problem on its own.

A less well-known cause is pelvic vein congestion. The growing uterus compresses the large veins in the pelvis, and pelvic blood flow can increase dramatically, with some sources reporting up to 60-fold congestion. If the resulting pressure backs up into the veins around the bladder, it can produce varicose veins on the bladder wall, a condition sometimes called cystovarix. These bladder varicosities can bleed, sometimes enough to produce visible blood in the urine or even difficulty emptying the bladder.⁹

A related vascular cause is nutcracker syndrome, where the left renal vein gets compressed between two major arteries. This condition can exist before pregnancy, sometimes producing intermittent blood in the urine that goes unexplained for years. Pregnancy can worsen it because the expanding uterus changes the pressure dynamics in the abdomen and pelvis. In reported cases, women with this condition experienced gross blood in their urine during pregnancy that resolved after delivery.¹⁰ Nutcracker syndrome is uncommon, but it is worth knowing about because it can mimic a kidney stone or infection and lead to unnecessary interventions if the clinician does not consider it.

Underlying Kidney Disease

For a small number of women, blood in the urine during pregnancy is the first sign that they have an underlying kidney condition. IgA nephropathy, the most common form of glomerulonephritis worldwide, is a good example. Women with this condition may have had episodes of blood in the urine that were never investigated, or they may have been diagnosed before becoming pregnant. Either way, pregnancy poses specific challenges. The disease shares features with preeclampsia, including high blood pressure and protein in the urine, which makes it difficult to tell the two conditions apart during pregnancy.¹¹

Women with IgA nephropathy also carry a substantially higher risk of actually developing preeclampsia, with one large cohort study finding more than a four-fold increase in risk. Because preeclampsia itself is a major driver of preterm birth and poor fetal growth, pregnancy in women with known kidney disease is managed as high-risk from the start.¹¹ An older but still-cited study of IgA nephropathy and pregnancy found that while most women’s kidney function followed a trajectory similar to women who never became pregnant, a small subset experienced rapid worsening that progressed toward kidney failure.¹²

The takeaway is not that pregnancy causes kidney disease, but that pregnancy can unmask or accelerate existing kidney problems. If you have persistent blood in your urine that is not explained by infection or stones, especially if protein is also showing up in your urine, a nephrologist may need to get involved.

Rare but Serious Causes

Urological cancers during pregnancy are genuinely rare, but they exist, and blood in the urine is often the presenting symptom. A review compiling all registered and published cases of renal and bladder cancer during pregnancy identified a total of 47 cases between 1999 and 2019. The most common symptom of bladder cancer in these cases was blood in the urine, reported in about two-thirds of patients. Renal cancer was more often flagged by pain.¹³

Diagnosis is often delayed because the symptoms overlap so heavily with normal pregnancy complaints. Flank pain, fatigue, and urinary changes are easy to attribute to the pregnancy itself. There are no specific guidelines for managing urological cancers discovered during pregnancy, so each case gets handled individually, weighing the risks of imaging, biopsy, and surgery against gestational age and the aggressiveness of the tumor.¹⁴ The rarity of these cases is itself a complicating factor: no single institution sees enough of them to develop standardized protocols. This is not something to lose sleep over, but it is one reason why persistent or unexplained blood in the urine should not be dismissed as “just a pregnancy thing” without at least basic workup.

When to Seek Help

Because of the wide range of possible causes, the practical question is not whether blood in your urine is abnormal during pregnancy, since mild microscopic blood often is harmless, but whether the pattern around it suggests something that needs attention. Some situations call for prompt evaluation:

Visible blood: Any urine you can see is pink, red, or dark brown warrants a call to your provider, even if it only happens once.
Fever or chills: Blood combined with a temperature above 100.4°F suggests the infection may have reached your kidneys, which can escalate quickly in pregnancy.
Severe flank or abdominal pain: This pattern points toward a kidney stone or, less commonly, a kidney infection.
Painful or burning urination: Classic cystitis symptoms alongside blood make a UTI the likely cause and treatment should start promptly.
Blood plus protein on a urine test: The combination raises concern for preeclampsia or underlying kidney disease and needs further evaluation.
Recurrent or persistent blood: Microscopic blood that keeps showing up across multiple prenatal visits, especially if it started before pregnancy, deserves a focused evaluation rather than ongoing monitoring without explanation.

A single episode of microscopic blood found on a routine dipstick, with no symptoms, a normal blood pressure, and no protein in the urine, is the scenario where watchful waiting is most appropriate. Your provider will likely repeat the test at your next visit and move on if it resolves. But if any of the features above are present, expect to be sent for a urine culture, blood work to check kidney function, and possibly an ultrasound to look at the kidneys and bladder.

False Positives and Practical Pitfalls

One thing that catches many pregnant women off guard is that blood on a urine dipstick does not always mean actual blood. Dipstick tests detect a molecule found in red blood cells, but the test can also react to myoglobin from muscle breakdown or be thrown off by highly concentrated urine. Vaginal bleeding or heavy discharge, both common in pregnancy, can contaminate a urine sample and produce a false positive. This is why a midstream, clean-catch sample is important, and why a positive dipstick is usually followed by microscopic examination of the urine sediment to confirm that red blood cells are actually present.

Even confirmed microscopic blood, as the large prospective study mentioned earlier showed, often leads to normal imaging and normal kidney function, with no impact on pregnancy outcomes.¹ The increased blood volume and kidney filtration rate of pregnancy mean that small amounts of red blood cells may spill into the urine under perfectly normal conditions. The challenge for clinicians is distinguishing this physiological leakage from the early stages of something that needs intervention, which is why the full clinical picture, not just the dipstick result, drives the decision.

If you are asked to provide a urine sample at a prenatal appointment and you know you are spotting vaginally, mention it before the test. A contaminated sample can trigger a cascade of follow-up tests and anxiety that could have been avoided with a simple heads-up. Some providers will ask you to return another day for a cleaner sample rather than chase a result that may not reflect what is happening in your urinary tract at all.

1
PubMed. Microscopic hematuria in pregnancy: relevance to pregnancy outcome
2
Obstetrics & Gynecology. Urinary Tract Infections in Pregnant Individuals
3
PubMed Central. Management of Kidney Stone Disease in Pregnancy: A Practical and Evidence-Based Approach
4
PubMed. The Risk of Preterm Birth in Low Risk Pregnant Women with Urinary Tract Infections
5
PubMed Central. Urinary tract infection during pregnancy and time relation to preterm birth-a Swedish observational study
6
PubMed Central. Risk of Early Birth among Women with a Urinary Tract Infection: A Retrospective Cohort Study
7
PubMed Central. Risk of Symptomatic Kidney Stones During and After Pregnancy
8
Nephrology Dialysis Transplantation. MO117THE IMPACT OF GESTATIONAL AGE ON ANATOMICAL AND PHYSIOLOGICAL CHANGES OF THE UPPER URINARY TRACT DURING PREGNANCY
9
American Journal of Obstetrics & Gynecology. Submucosal vesical varicosities causing hematuria and retention of urine in pregnancy: cystovarix
10
PubMed. Aggravation of the nutcracker syndrome during pregnancy
11
PubMed Central. Pregnancy outcomes in women with immunoglobulin A nephropathy: a nationwide population-based cohort study
12
PubMed. Pregnancy in IgA nephropathy
13
PubMed. Renal and Bladder Cancer During Pregnancy: A Review of 47 Cases and Literature-based Recommendations for Management
14
PubMed Central. Renal Cell Carcinoma in Pregnancy: A Case Report of a Rare Diagnosis