Screening for Asymptomatic Bacteria in the Urine during Pregnancy

Step 1: The Critical Appraisal - Reading & Recommendations

(Last review: March 2011)

Since the early 1950's there has been promotion of the idea that all pregnant women have urine tests for infection even though they have no symptoms. If infection was found, antibiotic treatment was given. As pregnancy advances, pressure from the growing baby prevents urine flowing freely from the kidney to the bladder. The reduction of urine flow could lead to kidney infections that would not normally occur. Infections in the kidney late in pregnancy could be serious for both mother and baby. Testing the urine at 16 weeks of pregnancy and treating the mother with antibiotics if necessary should prevent serious problems from developing.

Evidence

A number of studies have shown that women found to have bacteria in their urine at 12 to 16 weeks of pregnancy have a 13% chance of developing a serious kidney infections later in the pregnancy. Only 0.4% of women with sterile urine on testing at 16 weeks go on to develop an infection. Before antibiotics were available, women who suffered from kidney infections during pregnancy were much more likely to have babies with a low birth weight and had a higher risk of the baby dying during or shortly after birth.² The presence of bacteria in the urine at 16 weeks has been found to increase the chance of infant death 2.4 times that of women with sterile urine. Bacteria in the urine also lead to early labour and failure of the baby to grow during the pregnancy^.3

An analysis of many studies done on this subject (meta-analysis) found that women with bacteria in their urine had a 54% higher rate of labour before the end of pregnancy than women whose urine was not infected.⁴ Another study found that 40% of women with infected urine developed an infection in their uterus after the baby was born. ⁵ No study has found that a urinary tract infection during pregnancy causes permanent kidney damage or high blood pressure later in life.

Method of Urine Collection

A urine "dipstick test" for bacteria between 12 and 16 weeks is the most accurate way to test the urine for bacteria. If the first test indicates bacteria are present then a second test should be performed . If this test is positive then a sterile urine sample should be obtained and bacteria grown (cultured) so that the type of bacteria present may be identified and specific treatment given. This procedure will detect 80% of women with bacteria in their urine.⁶ It has been shown that further testing monthly provides little additional benefit.

Four studies have found that acute kidney infections were prevented in 20 to 30% of women who had bacteria detected by the urine dipslide procedure and had the bacteria eliminated by antibiotic treatment early in the pregnancy.^{1, 6, 7, 8} Although some investigators have questioned the cost effectiveness of the test, most agree that a single urine  test for bacteria between 12 and sixteen weeks of pregnancy is appropriate.⁹ A review demonstrated that the urine dipstick test alone seems to be useful in all populations to exclude the presence of infection if the results of both nitrites and leukocyte-esterase are negative. Sensitivities of the combination of both tests vary between 68 and 88% in different patient groups, but positive test results have to be confirmed. Although the combination of positive test results is very sensitive in family practice, the usefulness of the dipstick test alone to rule in infection remains doubtful.¹¹ The optimal duration of treatment is unclear but there is no evidence of difference in outcome between 3 and 7 days.  Given the uncertainty, short therapy with a follow up urine culture is reasonable.

The Critical Appraisal - Summary Recommendation

All pregnant women should undergo a single urine  test for bacteria between 12 and 16 weeks of pregnancy. If the test is positive, it should be repeated and a urine culture should be obtained. All women with bacteria present in their urine should be treated with appropriate antibiotics and have follow-up tests to insure that the urine is free of bacteria.

The Critical Appraisal - Other Recommendations

Both the U.S Preventive Services Task Force and the Canadian Task Force on the Periodic Health Examination agree with this recommendation. The Canadian task force gives screening for asymptomatic bacteria in pregnancy an "A" recommendation.

Selected References

1. Kinkaid-smith P, Buller M. Bacteriuria in pregnancy. Lancet 1965;i: 395-399.
2. Norden W, Kass EH. Bacteriuria of pregnancy – a critical appraisal. Ann Rev Med 1968; 19: 731-470.
3. McGrady GA, Darling JR, Peterson DR. Maternal urinary tract infection and adverse fetal outcomes. Am J Epidemil 1985; 121: 377-381.
4. Romero R, Oyarzum E, Mazor M, et al. Meta-analysis of the relationship between asymptomatic bacteriauria and preterm delivery/low birth weight. Obstet Gynecol 1989; 73: 576-582.
5. 5. Monif GRG. Intrapartum bacteriuria and postpartum endometritis. Obstet Gynecol 1991; 78: 245-248.
6. Stenqvist K, Dahlen-Nilson I, Lindin-Janson G, et al. Bacteriuria in pregnancy: 1. Frequency and risk of acquisition. Am J Epidemiol 1989; 129: 372-379.
7. Patterson TF, Andriole VT. Bacteriuria in pregnancy. Infect Dis Clin North Am 1987; 1: 807-822.
8. Little PJ. The incidence of urinary tract infection in 5000 pregnant women. Lancet 1966; ii (470): 925-928.
9. Campbell-Brown M, McFadyen IR, Seal DV, et al. Is screening for bateriuria in pregnancy worthwhile? Br Med J Clin Res Ed 1987; 294: 1579-1582.
10. Villar J, Lyndon-Rochelle MT, Gulmezoglu AM, Roganti A. Cochrane Data base Systematic Reviews 2000:CD000491
11. Devillé WL, Yzermans JC, van Duijn NP, Bezemer PD, van der Windt DA, Bouter LM The urine dipstick test useful to rule out infections. A meta-analysis of the accuracy. BMC Urol. 2004 Jun 2;4:4.

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