Last week, we published a paper which has been cooking for a long time. It is the result of years of hard work from particularly the first author – Tove Wikström – but also Sanna who did the bulk of the bioinformatic analysis with some help from me (well, I mostly contributed as a sounding board for ideas, but hopefully that was useful). The paper describes the gene expression of both the human host and the microbial community in the vagina during pregnancy and how the expressed genes (and the composition of bacteria) are linked to early births(1) and was published in Clinical and Translational Medicine.
We found 17 human genes potentially influencing preterm births. Most prominently the kallikrein genes (KLK2 and KLK3) and four different forms of of metallothioneins (MT1s) were higher in the preterm group than among fullterm women. These genes may be involved in inflammatory pathways associated with preterm birth.
We also found 11 bacterial species associated with preterm birth, but most of them had low occurrence and abundance. In contrary to some earlier studies, we saw no differences in bacterial diversity or richness between women who delivered preterm and women who delivered at term. Nor did Lactobacillus crispatus – often proposed to be protective against preterm birth (2,3) – seem to be a protective factor against preterm birth. However, most other studies have used DNA-based approaches to determine the bacterial community composition, while we used a metatranscriptomic approach looking at only expressed genes. In this context it is interesting that other metatranscriptomic results (4) agree with ours in that it was mainly microbes of low occurrence that differed between the preterm and term group.
Overall, the lack of clear differences in the transcriptionally active vaginal microbiome between women with term and preterm pregnancies, suggests that the metatranscriptome has a limited ability to serve as a diagnostic tool for identification of those at high risk for preterm delivery.