Background Trichomonas vaginalis is common worldwide, with high rates in women of reproductive age. The evidence-base on potential consequences of infection in pregnancy is mixed. We conducted a meta-analysis of studies which examined the association between T.vaginalis infection and adverse pregnancy outcomes.

Methods Following the PRISMA guidelines and MOOSE criteria, we searched the electronic databases Medline, EMBASE and BioMedCentral for articles published from January 1950 to February 2013; reference lists of published studies and reviews were also examined to locate additional eligible studies. The inclusion criteria were studies that assessed the statistical association between T.vaginalis in women and adverse pregnancy outcomes. The primary outcomes of interest were preterm birth, low birth weight and premature rupture of membranes. Meta-analysis methods were used to calculate a summary odds ratio for each outcome.

Results A total of 174 papers were identified, of these 48 full text papers were reviewed and 10 studies met the inclusion criteria. Six studies were cohorts, one a randomised control trial, one a case control study, one a population data linkage study and one a secondary analysis of combined data from four studies. The study populations, outcomes and study quality varied. The summary odds ratios (OR) was 1.4 (95% CI: 1.3–1.6, p = 0.0) for preterm birth (8 studies; n = 78,573) with negligible heterogeneity between studies (Isq. = 0.0%, p = 0.44). For low birth weight (3 studies; n = 14,660) the summary OR was 1.6 (95% CI: 1.1–2.2, p = 0.009) with low-moderate heterogeneity between studies (Isq. = 35.9%, p = 0.21) and the summary OR was 2.3 (95% CI: 0.9–6.2, p = 0.09) for premature rupture of membranes (4 studies, n = 14,715) with high heterogeneity (Isq. = 80.0%, p = 0.002).

Conclusion This review suggests that there is an association between T.vaginalis in pregnancy and preterm birth and low birth weight. These findings confirm the importance of screening for the infection, particularly in women of reproductive age in high prevalence areas.