Maintaining good oral hygiene may be especially important during pregnancy
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“Gain a child, lose a tooth,” says the proverb. We know that pregnancy is linked to an increased risk of dental problems, but we don’t really know why. Now, researchers have discovered that the oral microbiome changes while a woman waits, becoming less diverse and potentially more likely to cause inflammation.
Hormonal upheavals during pregnancy are commonly blamed for the higher risk of conditions such as gum disease and tooth decay. A common idea is also that fetuses take calcium from their mothers’ teeth, which is not supported by any evidence.
Disruptions to the oral microbiome, made up of more than 700 species of bacteria, can cause dental problems whether the person is pregnant or not. But Yoram Louzoun of Bar-Ilan University in Israel and colleagues wanted to understand whether this usually stable ecosystem changes during pregnancy, so they collected saliva samples from 346 Israeli women at 11-14 weeks, 24-28 weeks, and 32-38 weeks of pregnancy, representing all three trimesters.
The researchers found a decrease in species diversity in saliva samples starting at the transition between the first and second trimesters, and then gradually throughout pregnancy. Key features included a reduction in the number of species Akkermansia muciniphilaoften considered a “good bacteria”, and an increase in Gammaproteobacteria and Synergistota bacteria, linked to inflammation.
“In general, the oral microbiome is stable, but over the years its diversity slowly decreases,” explains Louzoun. “Pregnancy is like fast forwarding this very slow evolution. You can see the changes that normally happen over several years in just nine months.”
There are many possible reasons why these changes – although modest overall – are occurring. “A lot of things will happen during your pregnancy, like hormonal changes and inflammation, which will also change the microbiome,” says Lindsey Edwards of King’s College London. “And obviously during pregnancy you change your diet a lot. You may also feel nauseous and not eat, and you may also stop taking medications if you know you’re pregnant. All of that could have effects.”
The women completed questionnaires about their diet and health, which allowed researchers to identify distinctive, but similar, effects in some women, such as those who reported following a gluten-free diet, taking antibiotics, being stressed, or being current or former smokers. “Most women stop smoking when they’re pregnant, but you see the effect of the fact that they were smoking, maybe nine months ago, on the microbiome,” says Louzoun. “It has a very long-term effect.”
Comparable changes were evident in a second experiment, where researchers examined the oral microbiomes of 154 pregnant Russian women during their second and third trimesters.
Although pregnancy is known to increase the risk of dental problems, Louzoun doesn’t necessarily think that changes in the oral microbiome are the cause, given that such problems can appear very early in pregnancy. “I can’t really say whether all of these microbiome changes are positive or negative, but they’re certainly rapid,” he says.
Still, Edwards says microbial changes could be a factor, noting that saliva also becomes more acidic during pregnancy, changing its bacterial species.
Valentina Biagioli, from the University of Genoa in Italy, says changes in the oral microbiome and hormone levels throughout the body could both play a role, as they interact and influence each other. “There is a plausible biological rationale linking the observed changes in the oral microbiome to the most common dental problems reported during pregnancy, including tooth loss,” she says.
Disruptions to the oral microbiome have been linked to pregnancy complications, so if we establish what an optimal version of this ecosystem looks like, it could be used to assess the progress of a pregnancy. “Once we have the baseline oral microbiome of pregnancy, it can be used to detect deviations,” says Louzoun.
We are also learning more about the role of this microbiome in the immune system, which could affect the health of pregnant women and their fetuses. “The microbiome helps educate your immune system and is a two-way link,” says Edwards.
Better understanding how to maintain your oral microbiome – for example through good dental hygiene and a diverse, nutrient-rich diet – could therefore have lasting implications. “Changes in the microbiome could determine a parent’s inflammatory status and help strengthen the child’s immune system, either by inducing long-term health or by potentially impacting allergy risk, susceptibility to infections, or the development of long-term chronic inflammatory diseases,” says Edwards.
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