Why are urinary tract infections so common in pregnancy?

By (embryologist) and (embryologist).
Last Update: 07/10/2023

Urinary tract infections (UTIs) are quite common during pregnancy, occurring in 5-10% of all pregnancies. These infections may be symptomless, known as asymptomatic bacteriuria, but also include the more familiar cystitis and acute pyelonephritis.

Certain changes that a woman's body normally undergoes during pregnancy favor the occurrence of UTIs and, therefore, increase the risk of suffering from them. Therefore, it will be important to detect them, so that they can be adequately treated and do not affect either the woman or the baby.

Urinary tract infections and pregnancy

During pregnancy, many changes occur in a woman's body. Among them, those that occur normally in the urinary system of the pregnant woman favor the development of urinary tract infections (UTI). Therefore, there is an increased risk of contracting these types of infections in pregnancy. Among these changes are:

  • Dilatation of the ureters (the tubes that communicate the kidneys with the bladder).
  • Pressure on ureters and bladder due to the increasing size of the uterus.
  • Reduced muscle tone in the ureters.
  • Increased reflux from bladder to ureters.
  • Increased bladder volume.
  • Higher urine pH (urine becomes less acidic) and higher sugar content.

Urinary tract infections (UTI) involve a urine culture with a bacteriuria of more than 100,000 colony forming units (CFU) per milliliter. In general, the microorganisms that cause UTIs during pregnancy are the same as in non-pregnant women.

Types of urinary tract infection in pregnancy and symptoms

Three types of urinary tract infection can be distinguished, depending on the symptoms that the pregnant woman presents or the absence of symptoms. These are asymptomatic bacteriuria, cystitis and acute pyelonephritis.

Asymptomatic bacteriuria

Asymptomatic bacteriuria is the most common form of UTI, occurring in 2-11% of pregnancies. As its name suggests, it is characterized by the absence of symptoms, although there are bacteria in the woman's urine.

Even in the absence of symptoms, it is important to detect asymptomatic bacteriuria in pregnancy. Gestation can lead these asymptomatic bacteriurias to become complicated, resulting in acute pyelonephritis in 30-35% of the cases.

For this reason, when the pregnant woman undergoes a first trimester blood test, it is recommended that a urine culture is also performed to detect asymptomatic bacteriuria.

Thus, if the result is positive, antibiotic treatment will be given to the patient to reduce the possibility of pyelonephritis. Similarly, a new post-treatment urine culture will be performed to verify that it is already negative and, periodically, control cultures will be performed.

In addition, treatment of asymptomatic bacteriuria could reduce the rate of preterm delivery and low birth weight.


Cystitis occurs in approximately 1.5% of pregnancies and appears most frequently in the second trimester of pregnancy. These UTIs are quite recognizable because the woman notices symptoms such as:

  • Pain or burning when urinating.
  • Increased frequency of urination.
  • Sensation of needing to urinate urgently.
  • Pain in the upper pubic area.
  • Cloudy or even bloody urine.

In this case, a urine culture should be performed to confirm the diagnosis. However, antibiotic treatment can be started before the results are available to prevent the infection from worsening.

Once the treatment is completed, another urine culture will be performed after 7-15 days to verify that it is negative and, likewise, control urine cultures will also be performed.

Acute pyelonephritis

It is an infection in which the upper urinary tract and the kidney are affected, unilaterally (more frequently on the right side) or bilaterally. Acute pyelonephritis occurs in 1-2% of pregnancies, most commonly in those women who have had asymptomatic bacteriuria, especially if they have not undergone any type of treatment or it was inadequate.

Its onset is usually in the second or third trimester of gestation, causing symptoms such as the following:

  • Fever.
  • Sweating and chills.
  • Nausea and vomiting.
  • Intense and constant low back pain.
  • Alteration of the pregnant woman's general condition.

Because of its greater severity, acute pyelonephritis usually requires hospitalization of the pregnant woman. This will allow for an evaluation by the obstetrician, the necessary analyses and tests, and the initiation of intravenous antibiotic treatment as soon as possible.

Subsequently, follow-up includes a urine culture after completion of antibiotic treatment, as well as periodically (usually monthly).

FAQs from users

Does urinary tract infection during pregnancy suppose a risk?

By Andrea Rodrigo B.Sc., M.Sc. (embryologist).

During gestation there are a number of changes in a woman's body that can increase the chance of urinary tract infection. The risk lies in the fact that the infection spreads to the bloodstream and is dangerous to the fetus and mother. For this reason, it is common to test the urine during routine pregnancy check-ups.

The most prominent fetal risks are: premature birth, impaired fetal growth, low birth weight, or anemia in the baby.

Can a urinary tract infection in pregnancy be prevented?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

There are some tips that women can consider to try to avoid UTIs in pregnancy. These include:

  • Drink enough water to encourage urine production and urination.
  • Go to the toilet whenever necessary, without holding or holding back urine.
  • Always wipe the genital area from front to back.
  • Wear cotton underwear, which is more breathable, to avoid dampness.
  • Change wet bikinis or swimming costumes for dry clothes after swimming in a pool or at the beach.
  • Urinate after sexual intercourse.

However, if a urinary tract infection occurs during pregnancy, the woman should see a specialist as soon as possible so that the most appropriate treatment can be prescribed to avoid complications for her and her baby.

In the case of recurrences, the specialist can also prescribe preventive treatment to prevent infections from recurring.

Are there any natural remedies to treat urinary tract infection in pregnancy?

By Silvia Azaña Gutiérrez B.Sc., M.Sc. (embryologist).

When there is a urinary tract infection (UTI) in pregnancy, whether it is asymptomatic bacteriuria, cystitis or acute pyelonephritis, an effective antibiotic treatment should be prescribed, rather than trying to cure it with natural remedies.

The specialist will assess the best antibiotic and regimen for the woman, depending on the particular situation and always bearing in mind that the woman is pregnant.

Failure to treat a UTI properly could have consequences for both mother and baby.

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FAQs from users: 'Does urinary tract infection during pregnancy suppose a risk?', 'Can a urinary tract infection in pregnancy be prevented?' and 'Are there any natural remedies to treat urinary tract infection in pregnancy?'.

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Authors and contributors

 Andrea Rodrigo
Andrea Rodrigo
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information about Andrea Rodrigo
 Silvia Azaña Gutiérrez
Silvia Azaña Gutiérrez
B.Sc., M.Sc.
Graduate in Health Biology from the University of Alcalá and specialized in Clinical Genetics from the same university. Master in Assisted Reproduction by the University of Valencia in collaboration with IVI clinics. More information about Silvia Azaña Gutiérrez
License: 3435-CV

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