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Mycoplasma, bacterial vaginosis–associated bacteria BVAB3, race, and risk of preterm birth in a high-risk cohort

https://doi.org/10.1016/j.ajog.2013.10.003Get rights and content

Objective

Genital tract infection accounts for approximately 25-40% of all preterm 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 deoxyribonucleic acid was extracted from the Gram stain slides and analyzed using quantitative polymerase chain reaction.

Results

Among the 499 participants, Mycoplasma was positively correlated with increased risk of preterm (risk ratio [RR], 1.83; 95% confidence interval [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 the race/ethnic group and the presence of these and other individual taxa on risk of preterm birth. By contrast, bacterial vaginosis–associated bacteria (BVAB)-3 was consistently associated with a reduction in the risk of preterm birth for all racial/ethnic groups (0.55; 95% CI, 0.39–0.78).

Conclusion

BV is characterized by a reduction of Lactobacillus, and lactic acid–producing bacteria and the presence of Mobiluncus; we found these factors and the presence of Mycoplasma to be associated with an increased risk of preterm birth. By contrast, the presence of a recently identified organism sufficient to cause BV, BVAB3, decreased the risk of preterm birth. These findings give insight into why treating BV has mixed impact on risk of preterm birth.

Section snippets

Study population and sample collection

Vaginal fluid for Gram stains and clinical data were collected as part of a multicenter, randomized trial of ultrasound-indicated cerclage for preterm birth prevention.11 Women with a singleton gestation and at least 1 previous spontaneous preterm birth of 17-33 weeks' gestation were eligible for enrollment. Cervical length was measured at the initial sonographic cervical length evaluation, which was scheduled between 16 and 21 weeks' gestation. At the visit, a sterile speculum examination was

Results

As expected, because of the entry criteria of the study (at least 1 prior preterm birth; see Materials and Methods), the proportion of women with a preterm birth less than 37 weeks in this population was very high, with blacks having significantly higher rates of preterm birth than Hispanics or whites as well as significantly higher rates of cervical shortening (<25 mm). Smoking and douching habits also differed significantly by race (Table 1).

The overall prevalence of selected bacterial taxa

Comment

In an analysis of vaginal specimens collected from black, white, and Hispanic women at high risk of preterm birth between 17 and 22 weeks' gestation, we made several observations that give insight into the effect of selected vaginal taxa on the risk of preterm birth. First, we identified a protective effect of BVAB3 on the risk of preterm birth; BVAB3 was previously associated with BV.7 The effect was robust to adjustment for racial/ethnic group and cervical shortening to less than 25 mm. We

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      However, interventions targeting BV have been unsuccessful [6,8]. Next-generation sequencing technologies make it possible to characterize complex microbial communities associated with PTB [9–12]. However, findings from studies deploying these novel methods have been inconsistent, due in part to differences in study design, populations studied, and bioinformatics and statistical analytical techniques [2,13–15].

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      By sequencing the 16S ribosomal RNA gene, Hyman et al. showed temporal variability over the course of IVF treatment and a correlation between composition on the day of embryo transfer and live birth rate (Hyman et al. 2012). Foxman et al. found a significant correlation between the presence of species associated with bacterial vaginosis (Mycoplasma spp., Mobiluncus and Atopobium) and a higher risk of preterm birth (Foxman et al. 2014). In a study of 867 women undergoing IVF, Ralph et al. found a higher risk of early pregnancy loss in women with bacterial vaginosis, even though conception rates were not significantly decreased (Ralph et al. 1999).

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    This study was supported by grant R01 HD038098 from the National Institutes of Health (D.M. and B.F., principal investigators).

    The authors report no conflict of interest.

    Cite this article as: Foxman B, Wen A, Srinivasan U, et al. Mycoplasma, bacterial vaginosis–associated bacteria BVAB3, race, and risk of preterm birth in a high-risk cohort. Am J Obstet Gynecol 2014;210:226.e1-7.

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