From the Guidelines
For treating asymptomatic bacteriuria in pregnant women during the first trimester, nitrofurantoin (100 mg twice daily for 5-7 days) is typically the first-line antibiotic choice. This recommendation is based on the Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults 1. Alternatives include amoxicillin (500 mg three times daily for 3-7 days), amoxicillin-clavulanate (500/125 mg twice daily for 3-7 days), or cephalexin (500 mg four times daily for 3-7 days).
Key Considerations
- Treatment is essential despite the absence of symptoms because asymptomatic bacteriuria in pregnancy can progress to pyelonephritis and increase risks of preterm birth and low birth weight 1.
- The choice of antibiotic should be guided by urine culture and sensitivity results whenever possible.
- Trimethoprim-sulfamethoxazole should be avoided in the first trimester due to potential folate antagonism, and fluoroquinolones are contraindicated throughout pregnancy.
Follow-Up and Prophylaxis
- After treatment, a follow-up urine culture is recommended to confirm clearance of the infection.
- Some women with recurrent infections may require prophylactic antibiotics for the remainder of the pregnancy.
Rationale
The rationale behind this recommendation is supported by prospective, comparative clinical trials that have consistently reported that antimicrobial treatment of asymptomatic bacteriuria during pregnancy decreases the risk of subsequent pyelonephritis from 20%–35% to 1%–4% 1. Meta-analyses of cohort studies and randomized clinical trials also support the conclusion that antimicrobial treatment of asymptomatic bacteriuria decreases the frequency of low–birth weight infants and preterm delivery.
From the Research
Recommended Antibiotics for Asymptomatic Bacteriuria in Pregnant Women
The following antibiotics are recommended for treating asymptomatic bacteriuria in pregnant women in the 1st trimester:
- Nitrofurantoin: A study comparing a one- versus seven-day course of nitrofurantoin resulted in more persistent infection with the shorter course 2
- Ampicillin: A comparison of seven-day courses of 400 mg pivmecillinam versus 500 mg ampicillin showed no significant difference in persistent infection at two weeks or recurrent infection, but there was an increase in vomiting with pivmecillinam 3
- Cephalexin: A study comparing cephalexin 1 g versus Miraxid(R) (pivmecillinam 200 mg and pivampicillin 250 mg) given twice-daily for three days showed no significant difference in persistent or recurrent infection 3
- Fosfomycin trometamol: A study comparing a single dose of fosfomycin trometamol 3 g with a five-day course of cefuroxime showed no significant difference in persistent infection, shift to other antibiotics, or in allergy or pruritus 3
Duration of Treatment
The optimal duration of treatment for asymptomatic bacteriuria in pregnancy is not clear, but a short-course (four- to seven-day) regimen may be more effective than a single-dose regimen 2
- A short-course treatment was associated with a lower 'no cure' rate for asymptomatic bacteriuria in pregnant women, although there was evidence of statistical heterogeneity 2
- A single-dose regimen of antibiotics may be less effective than a short-course regimen, but more evidence is needed from large trials measuring important outcomes, such as cure rate 2
Screening and Diagnosis
Screening for asymptomatic bacteriuria is a standard of obstetrical care and is included in most antenatal guidelines 4
- All pregnant women should be screened for asymptomatic bacteriuria, and there are no new data that would indicate otherwise 4
- The optimal timing to screen for asymptomatic bacteriuria during pregnancy is not clear, but a study found no statistical difference according to the moment the urinary culture was done for the presence of asymptomatic bacteriuria 5