Trichomonas vaginalis is the most common curable sexually transmissible infection worldwide, with high rates in women of reproductive age. There have been inconsistent findings about the impact of infection and its treatment in pregnancy. We conducted a meta-analysis to determine the association between T. vaginalis and perinatal outcomes. Electronic databases were searched to May 2013. Included studies reported perinatal outcomes in women infected and uninfected with T. vaginalis. Meta-analysis calculated a pooled relative risk (RR) and 95% confidence interval (CI) using either a fixed- or random-effects model. Study bias was assessed using funnel plots. Of 178 articles identified, 11 studies met the inclusion criteria. The study populations, outcomes, and quality varied. T. vaginalis in pregnancy was associated with an increased risk of preterm birth (RR, 1.42; 95% CI, 1.15-1.75; 9 studies; n = 81,101; I 2 = 62.7%), preterm premature rupture of membranes (RR, 1.41; 95% CI,1.10-1.82; 2 studies; n = 14,843; I2 = 0.0%) and small for gestational age infants (RR, 1.51; 95% CI,1.32-1.73; 2 studies; n = 14,843; I2 = 0.0%). Sensitivity analyses of studies that accounted for coinfection with other sexually transmissible infection found a slightly reduced RR of 1.34 for preterm birth (95% CI, 1.19-1.51; 6 studies; n = 72,077; I 2 = 11.2%), and in studies where no treatment was confirmed, the RR was 1.83 (95% CI, 0.98-3.41; 3 studies; n = 1795; I2 = 22.3%). Our review provides strong evidence that T. vaginalis in pregnancy is associated with an increased risk of preterm birth. Based on fewer studies, there were also substantial increases in the risk of preterm premature rupture of membranes and small for gestational age infants. Further studies that address the current gaps in evidence on treatment effects in pregnancy are needed.