BACKGROUND AND PURPOSE:

• Bacterial vaginosis (BV) can now be identified using molecular techniques
• In asymptomatic non-pregnant North American women of reproductive age, there are 5 vaginal bacterial community state types (CSTs)
  • 4 of which are dominated by Lactobacillus species (CST I, II, III and V) and seen more frequently in Asian and White women
  • 1 (CST IV) that is more diverse, includes species associated with BV (Gardnerella and Mobiluncus) and is more commonly seen in Black and Hispanic populations
• The relationship between the vaginal microbiome and preterm birth remains controversial
• Tabatabaei et al. (BJOG, 2018) compared the vaginal microbiome between preterm and term deliveries

METHODS:

• Nested case-control study in a prospective pregnancy cohort
  • Singelton pregnancies
  • Women with either
    • Cases: Spontaneous preterm birth (<37 weeks) or
    • Controls: Term deliveries (≥37 weeks)
  • Vaginal microbiome was assessed by sequencing the V4 region of the 16S ribosomal RNA (rRNA) gene in swabs collected in early pregnancy
  • Relative abundance of bacterial operational taxonomic units, oligotypes, and vaginal CSTs were compared between groups
  • Estimated coefficient used for statistical analysis
    • Expected change in log relative abundance between women who developed early and late spontaneous preterm birth and those who had a term delivery

RESULTS:

• 94 cases of spontaneous preterm birth
  • 17 early (<34 weeks)
  • 77 late (34–36 weeks)
• 356 term deliveries (controls)
• Decreased risk of early but not late preterm birth was associated with
  • Lactobacillus gasseri/ Lactobacillus johnsonii (coefficient −5.36, 95% CI −8.07 to −2.65)
  • Lactobacillus crispatus / Lactobacillus acidophilus  (coefficient −4.58, 95% CI −6.20 to −2.96)
  • Lactobacillus iners / Ralstonia solanacearum  (coefficient −3.98, 95% CI −6.48 to −1.47)
  • Bifidobacterium longum/ Bifidobacterium breve (coefficient −8.84, 95% CI −12.96 to −4.73)
• Six vaginal CSTs were identified: four dominated by Lactobacillus; one with presence of bacterial vaginosis‐associated bacteria (Gardnerella vaginalis, Atopobium vaginae and Veillonellaceae bacterium) (CST IV); and one with nondominance of Lactobacillus (CST VI)
• CST IV was associated with increased risk of early (coefficient 4.22, 95% CI 1.24–24.85) but not late (coefficient 1.63, 95% CI 0.68–5.04) preterm birth, compared with CST VI
• There was a lack of association between the clinical Nugent score and vaginal microbiome composition

CONCLUSION:

• Lactobacillus gasseri/L. johnsonii, L. crispatus/L. acidophilus, L. iners/R. solanacearum and longum/B. breve may be associated with decreased risk of early preterm birth
• Molecular sequencing appears to be a more accurate reflection of the vaginal microbiome than the Nugent score

Learn More – Primary Sources:

Vaginal microbiome in early pregnancy and subsequent risk of spontaneous preterm birth: a case–control study

Related ObG Topics:

Bacterial Vaginosis – CDC Diagnosis and Treatment Recommendations

FDA Approves Secnidazole: Single-Dose Oral Treatment for BV

Do Hormonal Contraceptives Protect Against BV and Potential HIV Infection?