What does untreated BV lead to?

Untreated bacterial vaginosis is not usually serious, the NHS says, but it is linked to measurable risks: a higher chance of acquiring HIV (1.6-fold in the incidence studies of a 23-study meta-analysis), trichomoniasis (1.9-fold) and chlamydia, pelvic inflammatory disease, and in pregnancy a doubling of the odds of preterm birth and a small chance of miscarriage.^{1, 2, 3, 4} Most of the time, BV that's picked up and dealt with promptly doesn't lead to anything beyond the original discomfort. But leaving it, whether that's not seeking a diagnosis or not finishing a prescribed course, does carry real, well-documented risks. Here's the full rundown of what untreated BV has been linked to, with the numbers.

A higher chance of catching other infections, including HIV

BV disrupts the vagina's natural defences by making it less acidic, which makes it easier for other infections to take hold. The NHS says BV is not an STI but notes the small chance of complications and that sexual activity can trigger it or pass it on.¹ The research puts figures on the extra risk: in a meta-analysis of 23 studies and 30,739 women, BV was associated with a 1.6-fold higher chance of acquiring HIV in the studies that followed women for new infections; across 12 studies of 18,424 women, a 1.9-fold higher chance of trichomoniasis; and in 255 women exposed to a partner with urethritis, those with BV were 3.4 times as likely to test positive for chlamydia and 4.1 times for gonorrhoea.^{2, 3, 5} Whether BV itself should be considered sexually transmitted is a separate and unsettled question, which we've covered in Can BV mean STD?

Pelvic inflammatory disease (PID)

Pelvic inflammatory disease is an infection of the womb, fallopian tubes and ovaries. The NHS says it is usually caused by STIs such as chlamydia and gonorrhoea, but that it can also be caused by common bacteria that live in the vagina, and that if it is not treated early its complications include abscesses, long-term pelvic pain, problems with your fertility and a higher risk of ectopic pregnancy.⁶ Diagnosed early, the NHS says, PID is usually easily managed with antibiotics; pelvic pain alongside unusual discharge therefore needs an urgent GP appointment or NHS 111 rather than a wait.⁶

Fertility and IVF outcomes

Beyond PID, BV has also been linked to fertility problems, and the clearest figures come from a 2013 meta-analysis of infertility patients. BV was found in about 19% of women attending for infertility, was 2.8 times as common in women with tubal infertility as in women with other causes, and did not lower the chance of conceiving with IVF (odds ratio 1.03), but was associated with a 2.4-fold higher risk of very early pregnancy loss before a pregnancy was clinically confirmed.⁷ The authors counted the studies as few and small, so these are associations, not proof of cause. If you're undergoing or planning fertility treatment, that is reason enough to get any BV symptoms checked before starting, rather than assuming it's a minor, unrelated issue; some clinics swab for it before procedures and postpone if it is found.

Private vaginal or endometrial "microbiome tests" are a different matter. They report the proportions of bacteria in a sample, but there is no agreed healthy threshold for IVF, no trial showing that acting on the result improves outcomes, and a result such as "0% lactobacilli" is not a diagnosis of BV. Take the report to your fertility clinic or GP.

Pregnancy complications

This is one of the better-established risks. The NHS says BV in pregnancy carries a small chance of complications such as premature birth or miscarriage, while causing no problems in the majority of pregnancies.¹ In a meta-analysis of 32 studies with 30,518 women, BV without symptoms roughly doubled the odds of preterm delivery (odds ratio 2.16) and was linked to a higher risk of late miscarriage.⁴ Antibiotics clear BV in pregnancy and, in a Cochrane review of 21 trials, reduced late miscarriage, though they did not reduce preterm birth overall.⁸ The NHS asks anyone pregnant whose discharge changes to speak to a GP or midwife promptly.¹ Pregnancy care for all three infections, and what the NHS says is safe, is on BV, thrush and UTIs in pregnancy.

Before a procedure that opens the cervix

The NHS says PID caused by common vaginal bacteria is more likely after a coil fitting, a hysteroscopy, an abortion or any other procedure that opens up the cervix.⁶ If you have BV symptoms and one of these scheduled, mention it to the clinic beforehand rather than assuming it isn't relevant.

What untreated BV doesn't do

To be clear about what isn't on this list: BV does not transform into an STI, no matter how long it's left, and it doesn't spread through the body the way a systemic infection would. The risks above come from BV weakening your defences and creating opportunities for other problems, not from BV itself becoming something more dangerous. For how long BV typically takes to become a problem, and when it's worth escalating beyond home care, see What Happens If You Leave BV Too Long?

If you want to understand what's actually triggering your BV in the first place, we've broken that down in What Is The Main Cause Of BV?, the UK treatment routes are in How is BV treated in the UK?, and if it keeps coming back, Why do I keep getting BV? has the recurrence plan.

Frequently asked questions

Can BV cause bloating?

No. BV itself sits in the vagina; the NHS lists discharge and smell as its symptoms, and bloating is not one of them.¹ Bloating alongside unusual discharge, especially with pelvic pain, fever or pain during sex, points to something else, such as pelvic inflammatory disease, and needs a GP, a sexual health clinic or NHS 111 rather than a wait.⁶

Is bacterial vaginosis serious?

Usually not: the NHS calls it common and not usually serious.¹ It matters most in pregnancy, before a procedure that opens the cervix or fertility treatment, and when you may be exposed to an STI, because the risks above are real even if each is small.

How long can BV last if untreated?

Weeks to months. Some episodes clear on their own and many don't, and there is no reliable way to tell in advance which yours will be; the timeline is set out in What Happens If You Leave BV Too Long?, linked above.

Sources

1. NHS. Bacterial vaginosis. nhs.uk/conditions/bacterial-vaginosis.
2. Atashili J, et al. Bacterial vaginosis and HIV acquisition: a meta-analysis of published studies. AIDS, 2008. PubMed 18614873.
3. Seña AC, et al. Bacterial vaginosis and its association with incident Trichomonas vaginalis infections: a systematic review and meta-analysis. Sexually Transmitted Diseases, 2021. PubMed 34433796.
4. Leitich H, Kiss H. Asymptomatic bacterial vaginosis and intermediate flora as risk factors for adverse pregnancy outcome. Best Practice and Research Clinical Obstetrics and Gynaecology, 2007. PubMed 17241817.
5. Wiesenfeld HC, et al. Bacterial vaginosis is a strong predictor of Neisseria gonorrhoeae and Chlamydia trachomatis infection. Clinical Infectious Diseases, 2003. PubMed 12594649.
6. NHS. Pelvic inflammatory disease. nhs.uk/conditions/pelvic-inflammatory-disease-pid.
7. van Oostrum N, et al. Risks associated with bacterial vaginosis in infertility patients: a systematic review and meta-analysis. Human Reproduction, 2013. PubMed 23543384.
8. Brocklehurst P, et al. Antibiotics for bacterial vaginosis in pregnancy (Cochrane review). Cochrane Database of Systematic Reviews, 2013. PubMed 23440777.