A new study reveals that the oral microbiome undergoes significant shifts during pregnancy, becoming less diverse and potentially more inflammatory. These changes, observed in hundreds of women, may contribute to common dental problems like gum disease and tooth loss. Researchers suggest hormonal and lifestyle factors drive these alterations.
Pregnancy has long been associated with increased dental issues, encapsulated in the adage 'gain a child, lose a tooth.' While hormonal changes are often cited, a recent investigation points to upheavals in the oral microbiome as a key factor.
Yoram Louzoun at Bar-Ilan University in Israel led a study analyzing saliva samples from 346 pregnant women in Israel, collected at 11-14 weeks, 24-28 weeks, and 32-38 weeks, covering all trimesters. The findings, published on bioRxiv (DOI: 10.1101/2025.09.29.679276), show a decline in microbial diversity starting between the first and second trimesters, progressing through the pregnancy. Notably, levels of the beneficial bacterium Akkermansia muciniphila decreased, while inflammation-associated Gammaproteobacteria and Synergistota increased.
'Typically, the oral microbiome is stable, but over many years, there is a slow decrease in diversity,' Louzoun explained. 'Pregnancy is like a fast-forward of that very slow evolution. You can see the changes that normally happen over many years in just nine months.'
Similar patterns emerged in a second cohort of 154 pregnant women from Russia, examined during the second and third trimesters. Factors influencing these shifts include hormonal fluctuations, inflammation, dietary changes, nausea, and cessation of medications. Questionnaires revealed distinct effects among women on gluten-free diets, those taking antibiotics, experiencing stress, or with smoking history—even former smokers showed lingering impacts.
Experts offered mixed views on causality. Louzoun noted that while changes are rapid, their role in early-onset dental problems remains unclear. Lindsey Edwards at King's College London highlighted that pregnancy makes saliva more acidic, potentially exacerbating microbial shifts. Valentina Biagioli at the University of Genoa emphasized interactions between microbiome alterations and hormones, providing a 'plausible biological rationale' for issues like tooth loss.
These insights could inform pregnancy monitoring, with a baseline microbiome helping detect deviations linked to complications. Maintaining oral health through hygiene and diet might also support maternal and fetal immune systems, influencing long-term outcomes like allergy risks or chronic inflammation.