Background Several studies have shown that bacterial vaginosis (BV) is particularly prevalent in patients with infertility, though it has not been firmly established which risks infertility patients with BV incur for pregnancy outcome. We aimed to assess the prevalence of BV in infertility patients, as well as to quantify the magnitude of the association between BV and cause of infertility on the one hand, and conception rates and early pregnancy loss following in-vitro-fertilisation (IVF) on the other hand.

Methods Systematic literature review and meta-analysis.

Results The estimated prevalence of BV in infertile women is 19% (95% CI: 14 – 25%). Abnormal microbiota (Nugent scores 4 to 10) occurs in 39% of the infertile patients (95% CI: 26 – 52%). BV is significantly more prevalent in women with infertility compared to antenatal women in the same population (OR 3.32, 95% CI 1.53 – 7.20). BV is significantly more prevalent in women with tubal infertility compared to women with other causes of infertility (OR 2.77, 95% CI 1.62 – 4.75). BV is not associated with decreased conception rates (OR 1.03, 95% CI 0.79 – 1.33). BV is associated with a significantly elevated risk of preclinical pregnancy loss (OR 2.36, 95% CI: 1.24 – 4.51), but is not associated with an increased risk of first trimester abortion (OR 1.20, 95% CI: 0.52 – 2.74)

Conclusion All studies on cause of infertility in relation to BV included had a cross-sectional design and therefore do not allow for causal inferences. Still, there is strong circumstantial evidence that supports a causal link between BV and tubal infertility. Studies with a longitudinal design on other hand strongly support a relation between BV and early pregnancy loss. Unfortunately, no study looked beyond first trimester foetal loss.