It doesn't. Bacteria does, and you don't have to be preg to get a UTI. One of the best ways to avoid one is to pass all your urine completely and drink plenty of water.
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Attention Ladies, this is Suzi, many people have been writing in asking what the stuff was that I used to clear up my UTI last week, so I wanted to put the link to this stuff here
It is called CT - DM 
It doesn't. Bacteria does, and you don't have to be preg to get a UTI. One of the best ways to avoid one is to pass all your urine completely and drink plenty of water.
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different liquids in the body and or hormonal changes
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you don't always completely empty your bladder due to pressure from the baby therefore stale urine can build up leading to infection. Try once finished passing urine, stand up then sit back on the loo and try again, often another 30ml or so will come out.
Ensure you are drinking lots of water so are not dehydrated and making urine concentrated.
(on a side note, keep practicing your pelvic floor exercises but never while on the loo)
References :
obstetric physio
This is a great website.. good luck.
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http://www.americanpregnancy.org/pregnancycomplications/utiduringpreg.html
Little C's got it covered exactly right. Retained urine and dehydration (you need MUCH more water than you think while pregnant). Drink your body weight in water, an ounce per pound, at least, and then match up ounce for ounce any other liquids you ingest (soda, tea, milk) Your kidneys aren't just flushing your blood anymore, they are also flushing all the blood from your unborn child.
Drink d-mannose too, in moderation. Make sure it's not a punch or mix, they have added sugar or cornsyrup which defeats the purpose and feeds any bacteria. Also mixes have cut the amount of d-mannose in them, and aren't as effective.
Good luck.
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pregnancy doesnt cause UTIs. U can get that anytime in ur life men and woman. what causes them is a build up of bacteria like if u are holding ur pee to long. That is why it is good to drink lots of fluid especially water to flush out ur body of toxins but u have to actually go to the bathroom to flush it out. I know for me it gets really annoying when i feel like i am going to the bathroom like every other minute and u are temped especially at night to just lay there and hold it. But u have to go to avoid UTIs and other things. I have litterly been having to get up every single hour of the night just to go to the bathroom lately. I love it but i do it 99% of the time. im sure being preg can make it easyer to get them but preg does not cause it. good luck and God Bless
References :
How to Lose Weight with Acai Berry &How to Use Acai Berry for …: Urinary Tract Infection During Pregnancy … Ac… http://bit.ly/dmnQ4P
Aug 18, pregnancy and urinary tract infection http://goo.gl/fb/JldAn
Aug 18, pregnancy and urinary tract infection: I have had a urinary tract infection for about four days and my uri… http://bit.ly/cg1vQ5
yeah….iv had a nasty urinary tract infection throughout the pregnancy.I just googled it & frightened the crap outta me