Women's Healthcare Topics

Can a Urinary Tract Infection Cause Preterm Labor?

Reviewed by James Brann, M.D.

Bladder Infections Can Cause Pre-Term Labor

Throughout your pregnancy, it is important to be on the lookout for bladder infections, or urinary tract infections (UTIs). These bladder infections are quite common during pregnancy, affecting seven percent of all pregnant women.

Pregnant women are at a higher risk for urinary tract infections for several reasons. First, the high levels of progesterone in your body may relax the muscle tone of your ureters – the muscular tubes that connect the bladder to your kidneys. This hormonal reaction can cause your ureters to dilate, slowing down the flow of urine, which makes it easier for bacteria to reach your kidneys.

Secondly, as your uterus continues to grow in size during pregnancy, the added weight can compress your ureters, making it hard for urine to flow through them. Pregnancy also relaxes your bladder, making it prone to reflux – the bladder wall doesn't close completely when the bladder contracts, causing urine to flow back into your ureters. The back flow of urine brings with it bacteria that cause infections.

Each of these changes can result in bacteria multiplying and infecting your bladder and kidneys. This impurity can lead to bladder and kidney infections (called urinary tract infections). You should get treated as soon as possible if you contract a UTI during pregnancy to avoid potential complications such as pre-term labor.

There are two main types of urinary tract infections:

  • Cystitis: An infection of the bladder

  • Pyelonephritis: A kidney infection. This is the most serious type of UTI.

Urinary tract infections (UTIs) are common in pregnant women. By convention, UTI is defined either as a lower tract (acute cystitis – bladder infection) or upper tract (acute pyelonephritis – kidney infection) with symptoms.

Symptoms of a Urinary Tract Infection

During pregnancy, you may have a urinary tract infection and not even know it. The common symptoms of a urinary tract infection are:

  • A frequent or uncontrollable urge to pass urine

  • Pelvic pressure or lower abdominal pain

  • Pain, discomfort, and a burning sensation when you urinate

  • Urine that is foul smelling, or urine that looks cloudy

  • Blood in your urine

Because the frequent urge to urinate is often a regular pregnancy symptom, you may not even know that you have a urinary tract infection until your urine is tested at a regular prenatal visit. Not all women with urinary tract infections experience pain or stinging when they urinate, and not all women notice blood in their urine. Two percent of pregnant women have a urinary tract infection and do not realize they have one.

This is why your physician will check your urine at every prenatal visit. In the event that you have bacteria in your urine, you will be treated before any harm can be done. (When left untreated, the bacteria in your urine may increase your risk of going into labor before 37 weeks pregnant, or giving birth to a low birth weight baby).

When you're expecting a baby, you can help prevent urinary tract infections with the following measures:

Learn about Urinary Tract Infections During Pregnancy.
  • Keep yourself well hydrated. Drinking eight or more glasses of water a day may help flush out any bacteria in your urinary tract. Drinking cranberry juice can also be useful in fighting a bladder infection.

  • When you feel the urge, go right away. Don't hold it in! Always completely empty your bladder each time you urinate. Sometimes urination can push the bacteria from your bladder before it develops into a urinary tract infection.

  • After you use the bathroom, wipe from the front to the back. Wiping in the opposite way (back to front) after a bowel movement can cause bacteria to enter your urethra and lead to bladder infection.

  • During pregnancy, you will want to wear cotton underwear. Avoid wearing any tight underpants or tight pants – this can trap in moisture and lead to urinary tract infections.

  • You will want to avoid any douching or using strong soaps and feminine deodorant sprays "down there." All of these products can irritate your genital area and urethra, which makes it easier for bacteria to build up.

Asymptomatic Bacteriuria – Bladder Infection without Symptoms

Asymptomatic bacteriuria is a medical term that just means you have bacteria in your urine and you are not having any symptoms of a bladder infection.

Two percent of pregnant women have asymptomatic bacteriuria. Since you do not any have symptoms of a bladder infection, the only way to know you have a problem is when your physician checks your urine at each prenatal visit.

If your physician finds bacteria in your urine sample they will obtain a urine culture and will treat you with antibiotics. Treating you with antibiotics is very important to prevent a urinary tract infection from developing and the complications for your pregnancy that are associated with asymptomatic bacteriuria.

Asymptomatic bacteriuria during pregnancy has a greater propensity to progress to pyelonephritis (kidney infection) up to 40 percent than when not pregnant.

Bacteria found in your urine during pregnancy has been associated with an increased risk of preterm birth (delivery before 37 weeks), low birth weight (smaller than normal), and perinatal mortality (infant death). Studies have shown that treatment during pregnancy will greatly reduce these complications.

There are many antibiotics regimens that can be used to treat asymptomatic bacteriuria. The most popular treatments are listed:

  • Nitrofurantoin (Macrobid®) (100 mg orally every 12 hours for five days)

  • Amoxicillin (500 mg orally every 12 hours for three to seven days)

  • Amoxicillin-clavulanate (500 mg orally every 12 hours for three to seven days)

  • Cephalexin (500 mg orally every 12 hours for three to seven days)

  • Fosfomycin (3 g orally as a single dose)

Acute cystitis – Bladder Infection

Cystitis or bladder infection will have symptoms and it can occur alone or can be complicated by a kidney infection (pyelonephritis). The symptoms of a bladder infection include burning with urinations (dysuria), going to the bathroom frequently, a urgent feeling of the need to void, lower abdominal pain or suprapubic pain, and/or blood in your urine (hematuria).

No correlation has been established between a bladder infection in pregnancy and increased risk of low birth weight, or preterm delivery that is seen with asymptomatic bacteriuria, perhaps because pregnant women with bladder infection symptoms usually receive treatment.

Pregnant women with a bladder infection are treated with a three to seven day course of antibiotics as long as they do not have symptoms suggestive of a kidney infection.

The most common treatment regimens for a bladder infection are:

  • Nitrofurantoin (Macrobid®) (100 mg orally every 12 hours for five days)

  • Cefpodoxime (100 mg twice daily for three to seven days)

  • Amoxicillin-clavulanate (500 mg orally every 12 hours for three to seven days)

  • Fosfomycin (3 g orally as a single dose)

Pyelonephritis – Kidney Infection

A kidney infection (pyelonephritis) is characterized by pain in the side of your back below your ribs (flank pain), nausea/vomiting, fever (above 38ºC), and it may occur with or without symptoms of a bladder infection. As many as 30 to 40 percent of pregnant women with untreated asymptomatic bacteriuria will develop symptoms of a urinary tract infection, including kidney infection, during pregnancy. This risk is reduced by 70 to 80 percent if asympatomatic bacteriuria is treated.

Because of the higher risk of complications in pregnancy, pyelonephritis is treated with hospitalization and intravenous antibiotics until you do not have a fever for 24 hours and symptomatically improved.

When your fever is normal for 48 hours, you will be switched to antibiotics by mouth and continued for 10 to 14 days.


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