Causes of Frequent Urination During Pregnancy
The bladder is a balloon-shaped muscle that stores urine. Muscles under the bladder keep the urethra (the tube where urine leaves your body) closed and keep urine from leaking out.

The pressure of a full bladder signals your brain, giving you the “urge” to urinate. When you urinate, the muscles around the urethra relax and the bladder tightens to squeeze urine out.

During pregnancy, the pressure of your growing uterus may cause your bladder to send the message that it's full even when it's almost empty. Your body also contains more fluid during pregnancy. Your kidneys work harder throughout your pregnancy to flush waste products out of your body. All of these changes make you need to urinate more often.

As the uterus grows and rises higher during the second trimester, some women find that they don't have to urinate as frequently as before. However, when the baby moves lower to prepare for delivery, the pressure increases, causing even more frequent urination. During this time, the pressure may wake you up several times each night to urinate. It may also force some urine to leak out, particularly if the muscles around the urethra are not very strong. 

For the first few days after delivery, you may urinate even more often as your body gets rid of the extra fluid of pregnancy. But after a few days, your need to urinate should return to what it was before you became pregnant.

Frequent Urination: What You Can Do
Here are some tips for dealing with frequent urination or leaking during pregnancy:

• Avoid diuretics. Coffee, tea and colas that contain caffeine can make you urinate more frequently.
• Do Kegel exercises. These simple exercises can be done almost anywhere at any time. They strengthen the muscles that keep the urethra (the tube where urine leaves your body) closed. These exercises can help stop urine leaks. They may even help prepare these muscles for labor and delivery. Do these exercises by squeezing the muscles you use to stop the flow of urine and holding them for 10 seconds. Do this 10-20 times in a row at least three times a day.
• Don't drink fluids right before bedtime. To cut down on nighttime visits to the bathroom, drink your fluids earlier in the day. Cut back on how much you drink in the early evenings and nighttime. But be sure to drink adequate amounts of water and juice during the day to make sure that you are not robbing your body of vital fluids.
• Empty your bladder completely. To help prevent leaks, be sure that your bladder doesn't get too full. Try not to “hold it” when you feel the urge to urinate. This may mean more trips to the bathroom. When you urinate, try leaning forward a bit in order to completely empty your bladder. Always empty your bladder before exercising.
• Wear a sanitary pad or panty shield. A minipad or panty shield can catch unexpected leaks caused by coughing or sneezing.

When to Talk to Your Health Care Provider
Urinary tract infection is the most common infection in pregnant women. If left untreated, it can lead to more serious infection or preterm labor. Talk to your health care provider right away if you have any of these warning signs:

• Pain or burning when you urinate
• The urge to urinate again immediately after you empty your bladder.
• Fever
• Blood in the urine

Image source: National Kidney and Urologic Diseases Information Clearinghouse