Vaginal microbiome profiles provide clues about the risk of preterm birth
The presence of certain bacteria in the vaginal microbiota of pregnant women, combined with maternal characteristics such as age, may make it possible to stratify expectant mothers by obstetric risk and the risk of preterm birth.
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Far from remaining static during pregnancy, the vaginal microbiota evolves, and this change has been previously linked to the risk of preterm labor and preterm birth.
Despite this, the links between vaginal microbiota and preterm birth are far from clear: studies to date have been single-center, with contradictory findings, perhaps due to a lack of adjustments for confounding factors, such as the mothers’ ethnic background.
To get a clearer picture, a study 1 study utilized data from the geographically and demographically diverse US birth cohorts in the ECHO (Environmental influences on Child Health Outcomes) program, which was designed to study the impact of prenatal and early neonatal exposures on child health.
The researchers sought to use these cohorts to identify robust vaginal microbiota signatures during pregnancy which, when combined with maternal factors, could predict the risk of giving birth before 37 weeks of gestation.
<37 Preterm birth is defined as gestational age at birth of <37 weeks. ²
4-16% Across countries, the rate of preterm birth ranges from 4–16% of babies born in 2020. These findings illustrate the global scale of the risks associated with preterm birth. ²
13,4 million An estimated 13.4 million babies were born preterm worldwide in 2020. ²
Maternal factors associated to the risk of preterm birth
Of the 677 births analyzed, 12% (73) were preterm. The results show just how unequally women (mean age in study: 28 years) are affected by this risk.
- For example, 84% of preterm births involved women who identified as Black,
- and 85% were mothers with public health insurance only.
The risks of preterm labor and preterm birth thus appeared to be unevenly distributed according to maternal characteristics.
As regards the microbiota, women with a vaginal ( (sidenote: Community state types Five types of vaginal community have been identified, four dominated by lactobacilli (Lactobacillus crispatus, L. gasseri, L. iners, and L. jensenii) and a fifth characterized by a low lactobacilli content. ) ) dominated by lactobacilli other than L. iners were less affected by preterm birth. They accounted for 6.8% of preterm births and 28.8% of full-term births.
These findings suggest that a vaginal microbiota rich in Lactobacillus may be associated with greater vaginal stability during pregnancy.
900 000 Preterm birth complications are the leading cause of death among children under 5 years of age, responsible for approximately 900 000 deaths in 2019. ²
x3 Bacterial vaginosis is the most common lower genital tract infection and is associated with a 1.5- to 3-fold increase in risk for preterm labor. ¹
25-40% Up to 25–40 % of preterm births are considered infection-related. ¹
Bacteria at risk with predictive value
Risk assessments highlight an increased risk of preterm birth among women :
- with diverse non-Lactobacillus-dominant vaginal communities, or vaginal communities dominated by L. iners,
- compared to women predominantly harboring L. crispatus , which is considered more stable.
This holds true even after adjusting for ethnicity, maternal age, education level, or parity.
The researchers subsequently tried to predict this risk by testing several models. The best model combined the taxa Gardnerella vaginalis (associated with bacterial vaginosis), Prevotella timonensis, and L. crispatus with maternal factors (age, ethnicity, etc.). It achieved an
(sidenote:
AUC (Area Under the Curve)
A measure of a model’s ability to correctly distinguish between two classes (for example, “diseased” vs “healthy,” “positive” vs “negative”). It represents the area under a curve that plots the true positive rate (sensitivity) on the y-axis against the false positive rate on the x-axis. If the AUC equals 1, the model performs perfectly; above 0.80 it is generally considered very good, and above 0.90, excellent; at 0.5, it performs no better than random chance.
)
(area under the curve) of 0.77—a performance deemed satisfactory by the authors for a clinical prediction tool.
This study confirms that the vaginal microbiota, combined with maternal factors, could be used to create a predictive risk score for preterm birth across various US cohorts.
