Urine Infection in Pregnancy - Causes

Understanding the urinary tract

There are two kidneys, one on each side of the tummy (abdomen). They make urine which drains down tubes called ureters into the bladder. Urine is stored in the bladder. It is passed out through a tube (the urethra) which carries urine from the bladder when we go to the toilet.

Side view of female genitals and cross-section diagram of urinary tract

What causes a urine infection?

Most urine infections are caused by germs (bacteria) which come from your own bowel. They cause no harm in your bowel but can cause infection if they get into other parts of your body. Some bacteria lie around your back passage (anus) after you pass a stool (faeces). These bacteria can sometimes travel to your urethra (the tube from the bladder that passes out urine) and into your bladder. Some bacteria thrive in urine and multiply quickly to cause infection.

Women are more prone than men to urine infections, as their urethra is shorter and opens nearer the anus. Pregnant women are also more prone than non-pregnant women to urine infections. This is partly due to the hormonal changes of pregnancy which affect the urinary tract and tend to slow down the flow of urine. It also may be that the enlarged womb (uterus) presses on the bladder and prevents it draining as well. If urine does not drain quickly from the bladder, germs are more able to multiply and cause an infection.

Less commonly there may be other causes of a urine infection. If you have to have a tube (called a catheter) passed into your bladder, it is easier for germs to directly reach your bladder, and this may make urine infection more likely. Occasionally for people whose immune systems are not working well, the infection may spread through the bloodstream rather than up the urinary tubes.

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Author:
Dr Mary Harding
Peer Reviewer:
Dr Laurence Knott
Document ID:
4613 (v42)
Last Checked:
24 March 2016
Next Review:
24 March 2019

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.