Urinary Tract Infection in Pregnancy

Urinary tract infection, especially bladder infection, called cystitis, is a relatively common complication in pregnant women. Pregnancy causes hormonal and physical changes in the woman's body which, along with the difficulty with hygiene due to a distended belly, increase the frequency of urinary tract infections. In this text we will talk about the urinary tract infection in pregnancy.

We call a urinary infection any infection that attacks the kidneys, bladder and/or urethra. The infection of the kidneys is called pyelonephritis, bladder infection is called cystitis and urethral infection is urethritis.

Pregnant woman
Pregnant woman


Our urinary tract is usually sterile, that is, it does not contain germs. However, some people may have detectable bacteria in their urine test, called bacteriuria, without this necessarily indicating a urinary tract infection. The presence of bacteria in the urine without the occurrence of symptoms of urinary infection is called asymptomatic bacteriuria. In most people, asymptomatic bacteriuria has no clinical relevance and does not need to be treated. However, pregnancy is one of the few exceptions to this rule.

Pregnant women have a higher risk of developing a urinary tract infection when they have bacteriuria. Hormonal and urinary system changes favor urine reflux and dilation of the ureters, which increase the risk of bladder bacteria reaching the kidneys, causing pyelonephritis.

In addition to the increased risk of pyelonephritis, asymptomatic bacteriuria in pregnancy has been associated with an increased risk of preterm birth, low fetal weight and increased perinatal mortality.

Therefore, contrary to what happens in non-pregnant women, pregnant women indicate the presence of bacteria in the urine, even if they do not present with urinary complaints. If bacteriuria is detected, even if there is no cystitis or pyelonephritis, antibiotics are indicated to sterilize the urinary tract and prevent complications in pregnancy. If not treated in time, about 40% of pregnant women with asymptomatic bacteriuria will develop pyelonephritis.

Cystitis in pregnancy

Cystitis, bladder infection, occurs in approximately 1 to 2% of pregnant women. As the risk of ascent of the bacteria towards the kidneys is greater in the pregnant women, the cystitis of the pregnant woman is considered a more serious picture than the cystitis of the non pregnant women.

Cystitis in the pregnant woman is caused by the same bacteria as the common cystitis, with special emphasis on E.coli bacteria. The mechanism of contamination of the urinary tract by bacteria is similar to that occurring in non-pregnant women, with the aggravation that the enlargement of the uterus disrupts the emptying of the bladder, favoring the accumulation of urine longer than usual, which increases the risk of bacterial multiplication.

The symptoms of cystitis in pregnant women are the classic ones:
  • Pain or burning to urinate
  • Willing to urinate often
  • Difficulty in holding urine
  • Willing to urinate even with an empty bladder
  • Pain or feeling of heaviness in the bladder
  • Blood in the urine

Acute pyelonephritis in pregnancy

Pyelonephritis is the most common complication of the urinary tract in pregnant women, occurring in approximately 2% of all pregnancies.

As in cystitis, pyelonephritis is usually caused by E.coli bacteria. As already explained, the hormonal and physical changes of pregnancy favor the rise of bacteria from the bladder to the kidneys, causing infection of the same. Pyelonephritis is a much more serious infection than cystitis and can lead to severe sepsis, with circulatory shock and respiratory failure.

Pyelonephritis symptoms are fever, chills, and flank pain. Nausea, vomiting, and burning on urination may also be present.

As in cystitis, the diagnosis of pyelonephritis is also made through uroculture.


Every pregnant woman should collect uroculture on the first visit to the obstetrician or between the 12th and 16th week of gestation. It is also common for the obstetrician to request new uroculture in the third trimester.

Every pregnant woman with positive uroculture should be treated with antibiotics, regardless of whether or not they have symptoms. In pregnant women, asymptomatic bacteriuria is seen as a cystitis.

a) Asymptomatic bacteriuria or cystitis

Antibiotics of the quinolone class, such as ciprofloxacin, norfloxacin, and ofloxacin ( commonly referred to as types, resistance and indications ), are widely contraindicated in pregnancy. Bactrim should also not be used as a first choice.

Currently the safe options for treating asymptomatic bacteriuria or cystitis in pregnant women are:
  • Nitrofurantoin (Macrodantine) (100 mg orally every 12 hours for 5-7 days)
  • Amoxicillin (500 mg orally every 8 or 12 hours for 3-7 days)
  • Amoxicillin-clavulanate (500 mg orally every 12 hours for 3-7 days)
  • Cephalexin (500 mg orally every 6 hours for 3-7 days)
  • Fosfomycin (3 g orally in a single dose)

One week after the end of treatment the uroculture should be repeated to confirm the elimination of the bacteria. If the uroculture remains positive, the treatment should be repeated, this time for longer.

After the proven elimination of the bacteria, the uroculture should be repeated every month until the end of gestation.

Patients with more than two episodes of bacteriuria during pregnancy may benefit from a prophylactic treatment with macrodantine, a 100mg tablet daily, until the end of pregnancy.

In women with a history of repeat cystitis before pregnancy, the use of prophylactic antibiotics may also be used. In women with increased incidence of cystitis after sexual intercourse, a dose of postcoital antibiotics is indicated as a prophylactic measure.

b) Pyelonephritis

Based on the increased risk of complications in pregnant women, pyelonephritis has traditionally been treated with hospitalization and intravenous antibiotics until the patient is asymptomatic and afebrile for at least 48 hours. After this period the patient may be discharged with oral antibiotics to complete 14 days of treatment.

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