Why bacterial vaginosis keeps coming back

If BV keeps returning after antibiotics, that is the norm rather than a failure on your part. 50–80% of women relapse within 6–12 months of finishing treatment.

Two reasons, both now well characterized. First, biofilm: antibiotics prevent Gardnerella biofilm forming but cannot dismantle one already established. The concentration of clindamycin needed to eradicate biofilm exceeds 512 µg/mL in strains that are fully susceptible when free-floating, and around 68% of isolates resist metronidazole in recurrent disease.

Second — and this changed practice in 2025 — reinfection from a partner. A randomized trial found that treating the male partner alongside the woman cut three-month recurrence from 63% to 35%. The trial was stopped early for efficacy, and the accompanying editorial recommends clinicians treat male partners in recurrent BV (Vodstrcil & Bradshaw, NEJM 2025). If you have had repeated episodes and your partner has never been treated, that is worth raising.

Why it matters for fertility. BV more than doubles preterm birth risk (OR 2.19 across 20,232 patients) and is associated with preclinical pregnancy loss in IVF. Notably, treating BV during pregnancy does not reduce preterm birth — which argues for resolving it in the preconception window instead.