OBJECTIVE—Genital tract infection accounts for ~ 25–40% of all pre-term births. We sought to
assess the relationship between preterm birth and selected vaginal bacterial taxa associated with
preterm birth either directly or through their association with bacterial vaginosis (BV).
STUDY DESIGN—Vaginal fluid for Gram stain was collected between 17 and 22 weeks
gestation as part of a randomized trial of ultrasound-indicated cerclage for preterm birth
prevention in women at high risk for recurrent spontaneous preterm birth. Bacterial DNA was
extracted from the Gram stain slides and analyzed using quantitative PCR.
RESULTS—Among the 499 participants, Mycoplasma was positively correlated with increased
risk of preterm (RR = 1.83; 95% CI: 1.52,2.22) as was Mobiluncus (RR=1.36; 95% CI: 1.07, 1.73)
and Atopobium (RR=1.44; 95% CI: 1.1, 1.87). However, there were strong interactions between
race/ethnic group and the presence of these and other individual taxa on risk of preterm birth. By
contrast, BVAB3 was consistently associated with a reduction in risk of preterm birth for all
racial/ethnic groups (0.55; 95%CI: 0.39, 0.78).
CONCLUSIONS—BV is characterized by a reduction of Lactobacillus, and lactic acid
producing bacteria and the presence of Mobiluncus; we found these factors and presence of
Mycoplasma to be associated with increased risk of preterm birth. By contrast, the presence of a
recently identified organism sufficient to cause BV, BVAB3, decreased risk of preterm birth.
These findings give insight into why treating BV has mixed impact on risk of preterm birth.