TABLE 3.
Risk factors for preterm birth associated with the microbiome or microbial infections of the female reproductive tracta
| Classification | Risk factor(s) |
|---|---|
| Factors in the VMB | |
| Vaginal taxa increased in relative abundance in PTB | Aerococcus spp. (5, 15), Atopobium spp. (15, 226, 282), BVAB1 (5), BVAB2 (5), Chlamydia spp. (208), Clostridium sensu stricto (15), Coriobacteriaceae species (5), Dialister spp. (5, 15), Escherichia coli (208), Fusobacterium nucleatum (282), Gardnerella spp. (12, 147), GBS (208, 211), Klebsiella pneumoniae (208), BVAB3 (282), Megasphaera spp. (15, 226), Mobiluncus curtisii/Mobiluncus mulieris (226), Mycoplasma hominis (282), Olsenella sp. (15), Parvimonas sp. (5), Porphyromonas asaccharolytica (226), Prevotella spp. (5, 15, 148), Sneathia amnii (5), Sneathia sanguinegens (5, 226), TM7-H1 (5), Trichomonas vaginalis (208, 283), Ureaplasma spp. (81, 147, 209, 283) |
| Vaginal taxa reduced in relative abundance in PTB | Lactobacillus crispatus (5, 12, 14, 228, 229), Lactobacillus spp. (5, 12, 15, 147, 226, 227, 229) |
| Bacterial virulence factors | BV-associated bacteria: sialidase (199, 284); GBS: β-hemolysin/cytolysin (192) and hyaluronidase (193); unidentified taxa: lipopolysaccharide (285); unidentified taxa: volatile organic compound (286) |
| Bacterial load | A higher vaginal bacterial load is a risk for PTB recurrence (245) |
| Host factors associated with the VMB | |
| Host cytokines/chemokines | Amniotic fluid: IL-1β (287), IL-6 (184, 217, 287), IL-8 (184), IL-10 (218), and IL-18 (219); cervicovaginal fluid: IL-1β (5, 88), IL-6 (5, 216, 217), eotaxin (5, 225), and MIP-1β (5); plasma: GM-CSF (220) |
| Host antimicrobial peptide | Reduced β-defensin-2 (226) |
| Other factors | Short cervix (14, 234), cervical cerclage with braided suture (compared to monofilament suture) (236) |
| Microbial invasion | |
| Bacterial intrauterine infectionsb | Chlamydia trachomatis (204, 205), Escherichia coli (208, 209), Fusobacterium nucleatum (210), GBS (16, 208, 211), Klebsiella pneumoniae (207, 208), Mycoplasma hominis (204), Staphylococcus aureus (194, 209), Streptococcus mitis (209) |
| Viral infections | HIV (213, 288, 289), HPV (214) |
| Other sexually transmitted infections | Neisseria gonorrhoeae (289–291), Treponema pallidum (290), Chlamydia trachomatis (289, 291) |
a
Unless stated otherwise, risk factors show elevated concentrations/abundances in women who later experience PTB. BVAB1, “Candidatus Lachnocurva vaginae”; BVAB2, Lachnospiraceae BV-associated bacterium 2; BVAB3, Mageeibacillus indolicus; TM7-H1, “Candidatus Saccharibacteria” genomospecies TM7-H1; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.
b
Most of the vaginal taxa whose abundance increased in PTB were also reported as risk factors for intrauterine infections (174).