Treatment of Cystitis in Third Trimester Pregnancy
Nitrofurantoin monohydrate/macrocrystals (100 mg twice daily for 5 days) is the first-line treatment for cystitis in the third trimester of pregnancy, with cure rates of 87-89% and an established safety profile during this gestational period. 1, 2, 3
First-Line Treatment
- Nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days is the preferred agent, demonstrating clinical cure rates of 87-89% in pregnant women with cystitis 1, 4
- The American College of Obstetricians and Gynecologists confirms that nitrofurantoin may continue to be used as a first-line agent during the second and third trimesters for urinary tract infections 2, 3
- Nitrofurantoin should be avoided after 37 weeks of pregnancy due to theoretical risk of hemolytic anemia in the newborn 1
Alternative First-Line Options
- Cephalexin 500 mg every 12 hours for 7-14 days is an appropriate alternative, particularly if nitrofurantoin is contraindicated or unavailable 5, 1
- Amoxicillin and other cephalosporins may be used during pregnancy but carry a higher chance of therapeutic failure compared to nitrofurantoin 1
- Cefuroxime or amoxicillin-clavulanate for 7 days are considered second-line options when first-line agents cannot be used 1
Agents to Avoid in Third Trimester
- Trimethoprim-sulfamethoxazole should NOT be used in the last trimester of pregnancy due to potential contraindications, despite being effective in non-pregnant women 6, 7
- Fosfomycin trometamol, while effective in non-pregnant women, has limited safety data in pregnancy and is not routinely recommended 6, 1
- Fluoroquinolones should be avoided throughout pregnancy due to concerns about fetal cartilage development 6
Diagnostic Considerations
- Urine culture is mandatory in all pregnant women with cystitis symptoms before initiating treatment, unlike in non-pregnant women where empiric therapy without culture is acceptable 1, 8
- Asymptomatic bacteriuria should be screened at least twice during pregnancy, including in the third trimester, as all cases require treatment 1
- Significant bacteriuria is defined as ≥10⁵ CFU/mL in a midstream sample 1
Treatment Duration and Follow-Up
- Standard treatment duration for cystitis in pregnancy is 5-7 days, which is longer than the 3-day courses often used in non-pregnant women 5, 1, 4
- All pregnant women require post-treatment urine cultures to confirm bacterial eradication, as untreated infections can lead to serious maternal and fetal complications 1, 2
- If symptoms do not resolve or recur within 2-4 weeks, repeat urine culture and antimicrobial susceptibility testing should be performed 8
Critical Safety Principle
- Pregnant women should not be denied appropriate antibiotic treatment for cystitis, as untreated infections commonly lead to serious maternal and fetal complications, including pyelonephritis and preterm labor 2, 3
- The risk-benefit analysis strongly favors treatment with appropriate antibiotics over withholding therapy due to theoretical concerns 2, 3