Cervical pessary and cerclage placement for preterm birth prevention and cervicovaginal microbiome changes

Abstract

Introduction: Our objective was to compare the vaginal microbiome in low-risk and high-risk pregnant women and to explore a potential association between vaginal microbiome and preterm birth.

Material and methods: A pilot, consecutive, longitudinal, multicenter study was conducted in pregnant women at 18-22 weeks of gestation. Participants were assigned to one of three groups: control (normal cervix), pessary (cervical length ≤25 mm) and cerclage (cervical length ≤25 mm or history of preterm birth). Analysis and comparison of vaginal microbiota as a primary outcome was performed at inclusion and at 30 weeks of gestation, along with a follow-up of pregnancy and perinatal outcomes. We assessed the vaginal microbiome of pregnant women presenting a short cervix with that of pregnant women having a normal cervix, and compared the vaginal microbiome of women with a short cervix before and after placement of a cervical pessary or a cervical cerclage.

Results: The microbiome of our control cohort was dominated by Lactobacillus crispatus and inners. Five community state types were identified and microbiome diversity did not change significantly over 10 weeks in controls. On the other hand, a short cervix was associated with a lower microbial load and higher microbial richness, and was not correlated with Lactobacillus relative abundance. After intervention, the cerclage group (n = 19) had a significant increase in microbial richness and a shift towards community state types driven by various bacterial species, including Lactobacillus mulieris, unidentified Bifidobacterium or Enterococcus. These changes were not significantly observed in the pessary (n = 26) and control (n = 35) groups. The cerclage group had more threatened preterm labor episodes and poorer outcomes than the control and pessary groups.

Conclusions: These findings indicate that a short cervix is associated with an altered vaginal microbiome community structure. The use of a cerclage for preterm birth prevention, as compared with a pessary, was associated with a microbial community harboring a relatively low abundance of Lactobacillus, with more threatened preterm labor episodes, and with poorer clinical outcomes.

Keywords: 16S rRNA gene; cerclage; cervical length; community state type; microbial community; microbial diversity; microbial richness; pessary; vaginal bacterial load.

FIGURE 1

Flow chart of the study design.

FIGURE 2

Vaginal microbial community of healthy pregnant women in their second and third trimesters. (A) Taxonomic profiles of the swab samples at the second (first barplot from the bottom) and third trimester (second barplot from the bottom) for each participant based on sequence data of the 16S rRNA V4 region (V4‐16S). (B) Representation of clustering of the vaginal microbiome into the five Community State Types (CST I –V). (C) Microbial alpha‐diversity based on Chao1 and Shannon indices of the V4‐16S sequence data, (D) Bacterial load as assessed by amplification of the 16S rRNA gene using quantitative PCR.

FIGURE 3

Association between cervical length and microbial load, microbial diversity and Lactobacillus relative abundance at 20 WG. (A) Microbial load as assessed by amplification of the 16S rRNA gene V4 region using quantitative PCR for cervical length (CL) >25 mm and CL ≤25 mm. (B) Microbial alpha‐diversity as assessed by the Chao1 and Shannon indices on 16S sequence data for CL >25 mm and CL ≤25 mm (Chao1 index, P = 0.009; Shannon index, P = 0.15). (C) Correlation between CL and Lactobacillus relative abundance based on 16S rRNA sequence data (rho = 0.43, P = 0.04 for CL >25 mm).

FIGURE 4

Microbial diversity, load and CST over time. (A) Evolution of microbial alpha‐diversity according to the Chao1 and Shannon indices as fold‐changes between the second and third trimesters. Only the cerclage group showed a significant increase in microbial richness. (B) Increase in microbial load at around 30 WG in the cerclage group vs the pessary group. (C) Chao1 index at baseline vs gestational age at delivery plot, showing a negative correlation (Spearman test, rho = −0.24, P = 0.03). (D) CST shift over time. The shift to CST IV contributed to the significance (P = 0.01). (E) CST (I, II, III, V) shift to CST IV was higher in the cerclage group than in the control or pessary groups (odds ratio 15, Wald test, P = 0.005) and pessary (odds ratio 10.2, Wald test, P = 0.02) groups. Gray cells highlight the missing samples owing to PTB before week 30; green cells indicate no shift in CST; yellow cells indicate shift to any CST; orange cells indicate shift from any CST to CST IV.