Treatment of UTI at 28.5 Weeks Gestation
For a UTI at 28.5 weeks gestation, use cephalexin 500 mg four times daily for 7-14 days as first-line therapy, or alternatively amoxicillin-clavulanate if the pathogen is susceptible. 1
First-Line Antibiotic Options
Cephalosporins are the preferred choice at this gestational age, with cephalexin, cefpodoxime, or cefuroxime all being appropriate options that achieve adequate blood and urinary concentrations with excellent safety profiles. 1, 2
Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) is an appropriate alternative if the pathogen is susceptible based on culture results. 1, 3
Fosfomycin (single 3g dose) can be considered for uncomplicated lower UTIs, though clinical data for third trimester use is more limited than for cephalosporins. 1, 2
Critical Antibiotics to AVOID at 28.5 Weeks
Nitrofurantoin should NOT be used at this gestational age because it should be avoided in the third trimester due to risk of hemolytic anemia in the newborn. 1, 2
Nitrofurantoin also does not achieve therapeutic concentrations in the bloodstream and should never be used for suspected pyelonephritis. 1
Fluoroquinolones are absolutely contraindicated throughout pregnancy due to potential adverse effects on fetal cartilage development. 1, 2
Trimethoprim-sulfamethoxazole should be avoided in the third trimester due to risk of neonatal hyperbilirubinemia. 2
Treatment Duration and Monitoring
The total course of therapy should be 7-14 days to ensure complete eradication of the infection. 1
Always obtain a urine culture before initiating treatment to confirm diagnosis and guide therapy. 1, 2
Follow-up urine culture 1-2 weeks after completing treatment is recommended to confirm cure. 1
Special Considerations for Late Second/Early Third Trimester
Untreated UTI at this gestational age increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without treatment), and significantly increases risk of premature delivery and low birth weight. 1
If Group B Streptococcus (GBS) is identified on urine culture, the patient requires treatment at the time of diagnosis AND intrapartum GBS prophylaxis during labor, as GBS bacteriuria in any concentration is a marker for heavy genital tract colonization. 1
For severe infections or suspected pyelonephritis, initial parenteral therapy may be required with transition to oral therapy after clinical improvement. 1
Common Pitfalls to Avoid
Do not use nitrofurantoin after 28 weeks gestation - this is a critical timing distinction as it's safe earlier in pregnancy but contraindicated in late pregnancy. 1, 2
Do not use agents that lack bloodstream penetration for pyelonephritis - if there are any signs of upper tract involvement (fever, flank pain, systemic symptoms), cephalosporins or amoxicillin-clavulanate are essential. 1
Do not delay treatment - even asymptomatic bacteriuria must be treated in pregnancy to prevent progression to pyelonephritis and adverse pregnancy outcomes. 1