The Oral Microbiome and Pregnancy:
A Bidirectional Relationship
By Isabella Hampson
K21053811
6NNNRM05 Oral Biology
Word count: 2114
Introduction
, The oral microbiome represents a dynamic microbial community residing in the oral cavity. It
encompasses a diverse array of bacteria, viruses, fungi, and other microorganisms that play
crucial roles in maintaining oral, as well as systemic health1. Recent advances in Next
Generation Sequencing technology has allowed characterisation of this highly complex
ecosystem, providing valuable insights into its role in health and disease 2. Different species
of microorganisms occupy distinct niches within the oral cavity, including the teeth, tongue,
saliva, tonsils, gingival sulcus and hard and soft palates3. Commensal bacteria constitute a
healthy microbiome, however dysbiosis can occur when pathogenic populations become
overwhelming. This pathogenic shift can lead to development of two major oral infections:
periodontal disease, affecting the soft tissue that supports the teeth, and caries, affecting
the dental hard tissues4.
The human oral microbiome is shown to vary dramatically during different stages of life,
where in women, these variations can be observed during pregnancy. There have been
multiple studies conducted characterising these fluctuations in microbial flora in pregnant
women compared to non-pregnant women5-7, with data suggesting that pregnancy,
particularly during the first trimester, promotes the proliferation of microorganisms in the
oral cavity and facilitates colonisation of periodontal pathogens.
Evidence has shown that while microbial diversity is relatively unchanged, composition of
the oral microbiota undergoes a pathogenic shift during pregnancy which is believed to be
mediated by female hormones, progesterone and oestrogen6,8. This can put pregnant
women at risk of developing oral infections that may trigger periodontal disease. These
imbalances in oral microbial composition coupled with gingival inflammation have been
shown to contribute towards the occurrence of adverse pregnancy outcomes, such as low
birth weight, preterm birth9, preeclampsia, and miscarriages10. Pregnancy and the oral
microbiome have a bidirectional relationship, where aspects of pregnancy can influence the
composition and dynamics of the oral microbiota and conversely, the oral microbiota can
affect pregnancy outcomes. We will be exploring this relationship throughout this report.
The Oral Microbiome in Pregnancy
Pregnancy is characterized by profound immunological, hormonal, and metabolic changes
crucial for foetal development. These changes induce an ecological shift in the composition
of microorganisms in various locations of the body including the gut, vagina, and the oral
cavity2. Fujiwara et al. (2017) investigated oral bacteria composition in pregnant and non-
pregnant Japanese women, where polymerase chain reaction (PCR) analysis revealed
significantly higher microbial counts in pregnant women. They reported that incidences
of Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans and Candida species
in gingival sulcus (the space between the teeth and gums) during the first and second
trimesters of pregnancy were significantly higher than in the nonpregnant group 7. Consistent
with these findings, Carrillo‐de‐Albornoz et al. (2010) reported that the presence of both
