A urinary tract infection (UTI) is a very common health problem of pregnancy. A UTI can cause serious problems in pregnancy if it's not treated. Normal urine is sterile. It has fluids, salts, and waste products. It doesn't have bacteria, viruses, or fungi. The tissues of the bladder are kept apart from urine and toxic substances by a coating. This coating helps prevent bacteria from attaching and growing on the bladder wall.

The main parts of the urinary tract are:

• Two kidneys. These are purplish-brown organs that sit below the ribs toward the middle of the back.
• Two ureters. These are narrow tubes that carry urine from the kidneys to the bladder.
• Bladder. This is a triangle-shaped, hollow organ in the lower belly.
• Two sphincter muscles. These are circular muscles that help keep urine from leaking. They do this by closing tightly like a rubber band around the opening of the bladder.
• Urethra. This is the tube that allows urine to pass from the bladder to outside the body.

During pregnancy, normal changes happen in the way the urinary tract works. One change is that the kidneys grow larger. The growing uterus can also squeeze the ureters and bladder. During pregnancy, the bladder does not empty as well. The urine is not as acidic. It contains more sugars, protein, and hormones. All of these factors can increase the risk for a UTI.

Common types of UTIs include:

• Asymptomatic bacteriuria. This infection has no symptoms. It's often caused by bacteria that is in the woman's system before pregnancy. This type of infection happens in about 1 in 20 to 1 in 10 pregnant women. It may lead to acute bladder infection or kidney infection if left untreated.
• A urethral or bladder infection (acute urethritis or cystitis). This may cause symptoms including pain or burning with urination, frequent urination, urgent need to urinate, and fever.
• A kidney infection (pyelonephritis). Symptoms may include those of acute cystitis plus back pain. It may lead to preterm labor, severe infection, and adult respiratory distress syndrome.

The most common bacteria that causes UTIs is E. coli (Escherichia coli). It's normally found in the vagina and rectal area. Other bacteria may also cause UTI. These include group B streptococcus and sexually transmitted gonorrhea and chlamydia.

To diagnose a UTI, your doctor will take a full health history and give you a physical exam. You will also need urine testing and a culture for bacteria. Experts advise getting tested at the first prenatal visit and during pregnancy.

Treatment is important to prevent serious problems. You may need to take antibiotics. Women with pyelonephritis in pregnancy often need to stay in the hospital to get I.V. (intravenous) antibiotics.