Your kidneys filter water and other substances from your blood to produce urine. Urine production enables your body to rid itself of waste products and other potentially harmful substances, while also regulating water balance. During pregnancy, urine production increases -- as does the number of times you need to urinate each day. Urine normally has only a slight odor, so an increase or change in urine odor during your pregnancy might signal a problem.
Along with increased urine production, pregnancy also causes slight relaxation of the muscle tissue of your bladder and urethra -- the tube through which urine passes from your body. This can lead to some involuntary leakage of urine from your bladder, or urinary incontinence. This most often occurs when you sneeze, cough, laugh or strain. Less frequently, you might have difficulty holding when your urine and experience some leakage when you have to go. Even a small amount of leakage can cause a urine odor. Urine leakage is common during pregnancy, affecting 30 to 50 percent of women, according to the medical text "Maternal, Fetal, and Neonatal Physiology, 4th Edition." It can begin as early as your first trimester.
Urine usually has no little to no odor, but it does contain ammonia. This chemical is produced primarily by your kidneys from a byproduct of protein metabolism. The urinary concentration of ammonia is usually quite low because it's diluted by water. But if you're not drinking enough water and other fluids, your urine becomes more concentrated and may emit a strong ammonia odor. Increasing your fluid intake typically alleviates this problem and helps ensure that you don't become dehydrated -- which isn't healthy for you or your baby.
Urinary Tract and Vaginal Infections
The risk of contracting a urinary tract infection (UTI) increases during pregnancy. According to an October 2008 "European Journal of Clinical Investigation" review article, about 7.4 percent of pregnant women develop a UTI -- the most common infection during pregnancy. A UTI can cause a strong and unpleasant urine odor. Other possible symptoms include frequent or painful urination, fever and back pain, although some pregnant women experience no symptoms despite the presence of bacteria in the urine.
An infection of the vagina called bacterial vaginosis (BV) can also cause an unpleasant, sometimes fishy odor. Although the infection develops in the vagina, you might detect the odor when you urinate and vaginal secretions mix with urine. Although pregnancy does not increase your risk for BV, it's important to seek treatment as the condition heightens your risk for going into labor prematurely.
Next Steps and Precautions
If you're pregnant and notice an unusual urine odor, it's important to see your doctor to determine the cause and appropriate treatment. Certain problems are easily corrected. For example, drinking more fluids usually banishes the odor caused by concentrated urine. Use of panty liners and pelvic floor exercises can help if you have urinary leakage. A urinary tract or vaginal infection requires medical treatment as soon as possible. Call your doctor right away if you experience urine odor accompanied by fever, chills or back pain. These symptoms might signal a kidney infection, which requires immediate antibiotic treatment.