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 six-fold rise in late miscarriage.^{1, 2, 3, 4} BV that is dealt with promptly usually leads to nothing beyond the original discomfort, and the NHS says "half of women with bacterial vaginosis do not have any symptoms" at all.¹ But leaving it carries real, documented risks, none of which is BV itself becoming something else. This page is the evidence for each; the timeline, how long BV lasts and when to act, is on its sister page, What happens if you leave BV too long?

Evidence at a glance

• Largest pooling: 23 studies, 30,739 women; BV associated with 1.6 times the risk of acquiring HIV in the studies that followed women for new infections.²
• Pregnancy: 32 studies, 30,518 women; BV without symptoms doubled the odds of preterm birth (2.16) and raised the odds of late miscarriage six-fold (6.32).⁴
• Treatment in pregnancy: Cochrane review of 21 trials, 7,847 women; antibiotics cleared BV and cut late miscarriage (relative risk 0.20) but did not reduce preterm birth overall (0.88).⁸
• Not measured: no trial has left BV untreated on purpose, so every figure here is an association from women observed with and without it.

Sources checked on 29 October 2026.

Can BV cause bloating?

No. BV is a shift in the bacteria of the vagina, and the NHS lists its symptoms as "an unusual vaginal discharge that has a strong fishy smell, particularly after sex" and a change in colour and consistency, "greyish-white, thin and watery"; it "does not usually cause any soreness or itching", and it does not cause bloating, cramping, wind or weight gain.¹ Those are gut or period symptoms, and if they arrive in the same week as BV the two are coinciding, not connected; periods are themselves a common BV trigger, which is why the pairing feels real. The combination that does matter is bloating or lower tummy pain alongside unusual discharge, especially with fever, pain during sex or bleeding between periods: those are the NHS's symptoms of pelvic inflammatory disease, which needs an urgent GP appointment or NHS 111.⁶ A swab settles it either way, and sexual health clinics see you without a referral: how BV is tested.

Is untreated BV dangerous?

Not usually, in the NHS's words, but the same page says to see a GP or sexual health clinic if you think you have it, because "you may need to be treated with antibiotics".¹ The danger is indirect. BV makes the vagina less acidic and "reduces your natural defences against infection", so the long-term effects of untreated BV are the complications of other things it lets in: sexually transmitted infections, pelvic inflammatory disease, and problems in pregnancy.¹ Each is small for any one woman and documented across many. What untreated BV has been linked to, with the numbers:

A higher chance of catching other infections, including HIV

The NHS says BV is not an STI, but that it "increases your risk of getting an STI", 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, 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 "can be easily treated 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 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, did not lower the chance of conceiving with IVF (odds ratio 1.03), and 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 are planning fertility treatment, get any BV symptoms checked before starting; some clinics swab for it 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 the best-established risk. 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), raised the odds of late miscarriage six-fold (6.32) and of infection in the mother two and a half times (2.53).⁴ Treatment changes some of that: in the Cochrane review of 21 trials and 7,847 women, antibiotics cleared BV in pregnancy and reduced late miscarriage (relative risk 0.20), though they did not reduce preterm birth overall (0.88).⁸ The NHS asks anyone pregnant whose discharge changes to speak to a GP or midwife.¹ Pregnancy care for all three infections 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 is not relevant.

What untreated BV doesn't do

BV does not transform into an STI, however long it is left, and it does not spread through the body the way a systemic infection would: it is not a throat, bladder or blood infection. The one route by which vaginal bacteria cause trouble elsewhere is upwards, into the womb and tubes as PID, and only in some women.⁶ The risks above come from BV weakening your defences, not from BV itself becoming more dangerous. What triggers it is on What is the main cause of BV?, the UK treatment routes on How is BV treated in the UK?, and the recurrence plan on Why do I keep getting BV?

What we don't know

• Whether antibiotics for BV lower the risk of catching an STI. The associations are consistent, but no trial has tested that outcome; the 2008 meta-analysis called for one.²
• Whether BV causes tubal infertility or marks it. The studies were cross-sectional, so cause cannot be read from them.⁷
• Why antibiotics cut late miscarriage but not preterm birth. The Cochrane review found both results and could not explain the gap.⁸

Frequently asked questions

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 do not, and there is no reliable way to tell in advance which yours will be; the timeline and the points at which to act are on What happens if you leave BV too long?

Can untreated BV cause infertility?

Not directly. BV was 2.8 times as common in women with tubal infertility, which is the kind PID causes, but the studies cannot say which came first; it did not lower IVF conception rates.⁷ Untreated PID, which vaginal bacteria can cause, is the documented route to fertility problems.⁶

Can you get BV in your throat?

No. BV is defined by the balance of bacteria in the vagina and diagnosed on a vaginal swab. A sore throat after oral sex is a question for a sexual health clinic, which can test for the infections that do affect the throat.¹

Sources

1. NHS. Bacterial vaginosis. Page last reviewed 19 June 2026. nhs.uk/conditions/bacterial-vaginosis.
2. Atashili J, et al. Bacterial vaginosis and HIV acquisition: a meta-analysis of published studies. AIDS, 2008. Pooled analysis of 23 studies, 30,739 women; funding not stated in the abstract. 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. Pooled analysis of 12 studies, 18,424 women; two authors report fees from a diagnostics company. 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. Pooled analysis of 32 studies, 30,518 women. PubMed 17241817.
5. Wiesenfeld HC, et al. Bacterial vaginosis is a strong predictor of Neisseria gonorrhoeae and Chlamydia trachomatis infection. Clinical Infectious Diseases, 2003. Observational, 255 women. PubMed 12594649.
6. NHS. Pelvic inflammatory disease. Page last reviewed 17 December 2025. 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. Pooled analysis, 12 studies for prevalence and 2 to 6 per outcome; the authors call the numbers small. PubMed 23543384.
8. Brocklehurst P, et al. Antibiotics for bacterial vaginosis in pregnancy. Cochrane Database of Systematic Reviews, 2013. Cochrane review, 21 trials, 7,847 women; no conflicts known. PubMed 23440777.

General information, not medical advice. BV is diagnosed and treated by a GP or sexual health clinic; see one if you think you have it, and speak to a GP or midwife promptly if you are pregnant and your discharge changes.

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