UTI and pregnancy

The "urinary tract" consists of the various organs of the body that produce, store, and get rid of urine. These include the kidneys, the ureters, the bladder, and the urethra. Urinary tract can be infected from above (by bacteria entering the kidneys from the bloodstream and travelling downward) or from below (by bacteria entering the urethra and travelling upward). In older children and adults infection most often starts from below, and always happen when bacteria from the bowel that live on the skin near the rectum or in the vagina, which spread and enter the urinary tract through the urethra. Because of their physiological feature, women are more prone to get a UTI.

Does pregnancy make me more likely to get a UTI?
It's not clear that pregnancy increases your risk of cystitis, and there's a fair amount of research showing that pregnancy does not make you more likely to have asymptomatic bacteriuria. However, pregnancy greatly increases the risk of getting a kidney infection.
Here's why: Higher levels of the hormone progesterone decrease the muscle tone of the ureters (the tubes between the kidneys and the bladder), causing them to dilate and slowing the flow of urine. Plus, as your uterus enlarges it may compress the ureters, making it that much more difficult for urine to flow through them as quickly and as freely as usual.
Your bladder also loses tone during pregnancy. It becomes more difficult to completely empty your bladder, and your bladder becomes more prone to reflux, a condition where some urine flows back up the ureters toward the kidneys.
The upshot of these changes is that it takes longer for urine to pass through your urinary tract, giving bacteria more time to multiply and take hold before being flushed out, and it also becomes easier for the bacteria to travel up to your kidneys. What's more, during pregnancy your urine becomes less acidic and more likely to contain glucose, both of which boost the potential for bacterial growth.