Introduction

Pyuria is defined as the presence of white blood cells (WBCs) in the urine, which often indicates an underlying condition such as an infection or inflammatory process within the urinary tract. These conditions typically range from urinary tract infections (UTIs), asymptomatic bacteriuria (ASB), and other kidney-related disorders. 

For pregnant women, pyuria is a particular concern. Common causes include to both the mother and the foetus if left untreated. However, if it is detected early enough and the appropriate treatment, this can help avoid complications from developing or worsening.

The causes and risk factors of pyuria

How does pregnancy affect the urinary system? 

Pregnancy is one of the most physiologically demanding processes the body undergoes involving significant physical and hormone adaptations to support fetal development. The renal system is one of the key systems that is affected by these changes. Blood flow to the kidneys increases by up to 50%,¹ leading to more urine production to manage heightened metabolic waste. At the same time, hormonal changes cause the muscles in the urinary tract to relax, slowing urine flow and making pregnant women more susceptible to urinary tract infections (UTIs).^1,3,4 As the uterus grows, it puts pressure on the bladder, leading to frequent urination.¹ These changes help the body remove waste efficiently but also while also raise the risk of kidney swelling (hydronephrosis) and transient proteinuria due to fluid retention, which doctors monitor closely to prevent complications.¹ In addition to this, the increased rate of urine production also leads to elevated urine pH and glucose concentration, further predisposing pregnant women to UTIs.

Urinary tract infections (UTIs) and their role in pyuria

UTIs are typically the leading factor in causing pyuria as they are one of the most common complications experienced during pregnancy. Hormonal and physiological changes, such as urinary stasis (slowed urine flow) and ureteral dilation (widening of the ureters), create an environment conducive to bacterial growth. These changes allow bacteria to ascend more easily through the urethra, increasing the risk of infection in the bladder (cystitis) or kidneys (pyelonephritis), the latter of which poses serious risks to both maternal and fetal health.⁴ 

UTIs can be sorted into 2 different types depending on where the infection happens.

• Lower UTI (Cystitis or Asymptomatic Bacteriuria): Infection confined to the bladder
• Upper UTI (Pyelonephritis): Infection involving the kidneys, a more severe condition requiring urgent treatment⁵

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The severity of the infection depends largely on its location. Lower UTIs (e.g., cystitis or asymptomatic bacteriuria) are generally less severe and often resolve within 1–2 weeks with appropriate antibiotics.⁴ Symptomatic UTIs present similarly in pregnant and non-pregnant individuals, with common signs including:

• Dysuria (pain or burning during urination)
• Urinary frequency (needing to pee more often)
• Abnormal urine appearance (cloudy or bloody urine)
• Fever or chills

Complications arise when a pregnant individual has asymptomatic bacteriuria (ASB) a condition where significant bacteria colonize the urine without symptomsof a UTI.^2,4,5 If untreated, ASB can progress to pyelonephritis (kidney infection), which is associated with serious complications such as preterm labor or sepsis. The symptoms include:

• Pain in the lower back or side
• A fever of 38°C
• Chills⁴ 

ASB needs to be tested in pregnant individuals early to prevent the risk of pyelonephritis. Patients who have a history of frequent UTIs, have experienced ASB in prior pregnancies, or who are diabetic are at a higher risk of developing a UTI; therefore should be prioritised in having ASB or UTI tested.⁴ Because pregnancy itself can mimic UTI symptoms (e.g., frequent urination), diagnosis requires confirmatory testing, such as urinalysis and urine culture

A urine dipstick test is a rapid diagnostic test used to detect UTIs.³ The test consists of a small paper strip with chemically treated colourimetric pads. When immersed in urine, these pads react with specific substances (e.g., leukocyte esterase, nitrites) and undergo characteristic color changes that indicate possible infection (e.g. positive leukocytes/nitrites) or normal results (no significant biochemical markers)

Urine culture testing 

This is where a sample of the urine is tested to see if there are certain cells present in the urine that indicate that the patient has a UTI. There are two types of cultures that can be performed - a urine sediment culture and a urine culture.³ A urine sediment culture is where urine is spun in a centrifuge. This allows for the solid pieces in the urine that cannot be seen by the naked eye to collect at the bottom of a test tube. The collection of cells at the bottom is then examined under a microscope to see what it is made up of. If there is a certain number of WBCs or bacteria, that is an indicator of a UTI.^2,3

A urine culture is a final test to see if bacteria grow from a sample taken from the urine. It is placed on a separate dish and left for up to five days. If bacteria does grow, that means a UTI is present. 

How do these infections affect both the pregnant individual and the foetus?

There are a multitude of complications that could occur to both the pregnant individual and the foetus if the pyuria is not noted and the infection is left untreated. For the fetus, complications may include:

• Preterm Birth (delivery before 37 weeks) 
• Low birth weight
• Neonatal infection transmission 
• Perinatal death (death of the baby at birth)^2,3,5,6

However, the pregnant individual could suffer from more complications during the pregnancy if the infection is left untreated. If the ASB is left untreated, as mentioned earlier, this could eventually develop into pyelonephritis - a life-threatening kidney infection. This is especially dangerous for pregnant individuals, as their immune system has changed as a result of the pregnancy, making their bodies less capable of fighting the infection. Complications in expectant individuals include:

• Sepsis
• Disseminated intravascular coagulation
• Pre-eclampsia
• Polyhydramnios
• Renal failure
• Acute respiratory distress syndrome (ARDS)^5,6

Inappropriate antibiotic use during pregnancy, including overuse or incorrect prescribing may lead to significant complications.³ These risks include the child could potentially develop cerebral palsy, onset sepsis with antibiotic-resistant microorganisms, malformations and epilepsy.³

How can we treat pyuria and prevent it from happening?

The treatment and prevention of pyuria lie in the treatment and prevention of the infection that causes it. There is an importance placed on the prevention strategies for UTIs as this eliminates the use of antibiotics but also the infection taking place at all. Most prevention protocols involve screening the pregnant individual early on during pregnancy to check if they have ASB or show any signs of a UTI, especially in people who are at a high risk.^3,4 Other prevention strategies include promoting hygienic practices in the hospital, encouraging patient education on adequate and to urinate regularly to prevent the growth of bacteria.⁴ 

If the infection does take place, the antibiotics used must be safe for pregnant individuals to consume to prevent any harm towards the foetus, which includes:

• Amoxicillin
• Cephalexin
• Nitrofurantoin 
• Avoiding fluoroquinolones and tetracyclines due to fetal toxicity risks

Summary

Pyuria is a key indicator of urinary tract infection in pregnancy, requiring prompt intervention to prevent serious maternal and fetal complications. Left untreated, these infections may lead to adverse outcomes including preterm delivery, low birth weight, and perinatal mortality. This underscores the vital importance of early detection through routine prenatal screening and consistent antenatal care. Fortunately, effective prevention remains achievable through simple yet essential measures: maintaining proper hydration, practising good genital hygiene, and attending regular medical check-ups. Through these combined efforts of vigilance, prevention, and timely treatment, healthcare providers can significantly improve pregnancy outcomes and safeguard both maternal and neonatal health.