Urinary Tract Infection in Pregnancy

Lower urinary tract infection involves infection in the bladder, causing cystitis (inflammation of the bladder). Upper urinary tract infection involves infection up to the kidneys, called pyelonephritis.

Pregnant women are at higher risk of developing lower urinary tract infections and pyelonephritis.

Urinary tract infections in pregnant women increase the risk of preterm delivery. They may also increase the risk of other adverse pregnancy outcomes, such as low birth weight and pre-eclampsia.


Asymptomatic Bacteriuria

Asymptomatic bacteriuria refers to bacteria present in the urine, without symptoms of infection. Pregnant women with asymptomatic bacteriuria are at higher risk of developing lower urinary tract infections and pyelonephritis, and subsequently at risk of preterm birth.

Pregnant women are tested for asymptomatic bacteriuria at booking and routinely throughout pregnancy. This involves sending a urine sample to the lab for microscopy, culture and sensitivities (MC&S).

Testing for bacteria in the urine of asymptomatic patients is not recommended as it may lead to unnecessary antibiotics. Pregnant women are an exception to this rule, due to the adverse outcomes associated with infection.



Lower urinary tract infections present with:

  • Dysuria (pain, stinging or burning when passing urine)
  • Suprapubic pain or discomfort
  • Increased frequency of urination
  • Urgency
  • Incontinence
  • Haematuria


Pyelonephritis presents with:

  • Fever (more prominent than in lower urinary tract infections)
  • Loinsuprapubic or back pain (this may be bilateral or unilateral)
  • Looking and feeling generally unwell
  • Vomiting
  • Loss of appetite
  • Haematuria
  • Renal angle tenderness on examination


Urine Dipstick

Nitrites are produced by gram-negative bacteria (such as E. coli). These bacteria break down nitrates, a normal waste product in urine, into nitrites. The nitrites in the urine suggest the presence of bacteria.

Leukocytes refer to white blood cells. There are normally a small number of leukocytes in the urine, but a significant rise can be the result of an infection, or alternative cause of inflammation. Urine dipstick tests examine for leukocyte esterase, a product of leukocytes, which gives an indication to the number of leukocytes in the urine.

Nitrites are a more accurate indication of infection than leukocytes.

During pregnancy, midstream urine (MSU) samples are routinely sent to the microbiology lab to be cultured and to have sensitivity testing.



Most common cause of urinary tract infection is Escherichia coli (E. coli). This is a gram-negative, anaerobic, rod-shaped bacteria that is part of the normal lower intestinal microbiome. It is found in faeces, and can easily spread to the bladder.

Other causes:

  • Klebsiella pneumoniae (gram-negative anaerobic rod)
  • Enterococcus
  • Pseudomonas aeruginosa
  • Staphylococcus saprophyticus
  • Candida albicans (fungal)



Urinary tract infection in pregnancy requires 7 days of antibiotics.

The antibiotic options are:

  • Nitrofurantoin (avoid in the third trimester)
  • Amoxicillin (only after sensitivities are known)
  • Cefalexin


Nitrofurantoin needs to be avoided in the third trimester as there is a risk of neonatal haemolysis (destruction of the neonatal red blood cells).

Trimethoprim needs to be avoided in the first trimester as it is works as a folate antagonist. Folate is important in early pregnancy for the normal development of the fetus. Trimethoprim in early pregnancy can cause congenital malformations, particularly neural tube defects (i.e. spina bifida). It is not known to be harmful later in pregnancy, but is generally avoided unless necessary.


Last updated September 2020
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