Preterm birth and perio link debunked

March 1, 2012
Harvard Square was where I decided to stay while attending a one-week intensive course on evidence-based dentistry (EBD) late in 2011.

Harvard Square was where I decided to stay while attending a one-week intensive course on evidence-based dentistry (EBD) late in 2011. The course was sponsored by the American Dental Association’s Center for Evidence-Based Dentistry in collaboration with the Forsyth Institute in Cambridge, Mass. I felt like a kid in a candy store the entire time, partly because I treated myself every day to a slice of pizza with a thin, crispy crust and a chocolate fudge coffee gelato.

Intellectually and socially, I was treated to an experience of a lifetime, thanks to Dr. Richard Niederman and his cadre of truly outstanding evidence-based educators, including Julie Frantsve-Hawley, RDH, PhD, the director of the ADA Research Institute and Center for Evidence-Based Dentistry.

The Forsyth Institute has a solid history of scientific research and, apart from the ADA Center for Evidence-Based Dentistry, is the most important resource for dental professionals who want to learn to manage information and improve the quality of care they deliver.

Course participants were mainly dentists — GPs and specialists, dental school faculty, and government employees. Because of my nerdy disposition, I love being a student but I was immediately engaged during breakout sessions where we were challenged individually to analyze published research reports for validity and applicability. Trust me, this is no easy topic and it takes a lot of hard work to learn to distinguish between quality research evidence (best evidence) and poor quality studies. In answering clinical questions (called PICO questions), what is required is evidence from the most appropriate study design to answer the question being posed.

As an example of how difficult it is to filter best available evidence from a large volume of research on a given topic, I decided to interview Frieda Pickett, RDH, MS, a distinguished professor of dental hygiene and an exacting professional who takes EBD very seriously. The topic I chose was the history of a statistical link between periodontal disease and preterm birth/low birthweight babies. Follow along, and Frieda will walk you through the process of what’s needed to build strong evidence in establishing cause and effect.

Slim: Researchers over the last decade have been studying the relationship between periodontal disease (PD) and preterm/low birthweight outcomes. Where did these observations begin?

Pickett: The first epidemiological study to determine if there was an association between PD and preterm birth was completed by Offenbacher et al. (1996) and faculty at University of North Carolina, School of Dentistry.1 Later, M. Jeffcoat completed a pilot study (2003) and reported that periodontal treatment may reduce preterm birth; however, she also emphasized that larger studies were needed to demonstrate statistical significance.2 Her study design was such that she could state the results only applied to the subjects in her study. She spoke at the Southwest Dental Conference in Dallas about the study and gave the audience the aforementioned information.

Slim: What is the status of the link between preterm/low birthweight and periodontal disease now that we’ve had several years to study it?

Pickett: There are two recent systematic reviews (SRs) assessing the best evidence for determining if periodontal treatment reduces the incidence of various adverse pregnancy outcomes. One of the reviews was published in a U.S. publication3 and the other was published in the United Kingdom.4

In the JADA (U.S.) review, 10 randomized controlled trials (RCT) met the criteria for studies of preterm birth (PTB), and eight RCTs met criteria for low birthweight (LBW). The overall odds ratio of PTB in the treatment group was 0.589 (95% confidence interval [CI] = 0.396-0.875) and of low birthweight (LBW) was 0.717 (95% CI = 0.440-1.169). Both ratios were less than 1, indicating no effect. The clinical implication reported in this SR was stated as follows: “Pooled results from the highest-quality RCTs do not support the hypothesis of a reduction of PTB or LBW in women who are treated for periodontal disease during pregnancy.”3

Of the 11 trials in the British Medical Journal SR, five were considered to be of high quality and low bias, while six were categorized as low quality with a high chance of bias.4 The U.K. SR concluded that the low quality trials supported the concept that treatment for periodontal disease had positive effects on pregnancy outcomes. The high quality studies, however, showed that treatment resulted in no significant effect on the rate of preterm births.

Much has been written using studies that showed associations between periodontal infection/inflammation with adverse pregnancy outcomes, of which preterm birth is included. The National Institutes of Health funded a large multicentered cohort study to determine if the association was true and not a spurious association.

The group assessed the risk of adverse pregnancy outcomes (preterm birth [PTB], preeclampsia [PRE], fetal growth restriction [FGR], or perinatal death) in women with periodontal disease (PD) compared to those without PD. Data was gathered from three sites. The conclusion stated that “there is no association between periodontal disease and adverse pregnancy outcomes.”5

Slim: In studying oral/systemic links, what kind of evidence is required to support/reject them?

Pickett: Trials with the least risk for bias, such as randomized controlled trials, provide the highest level of, or best evidence. Trials which are multi-centered and have a large sample size with adequate power to determine a judgment regarding the results of the study are considered to be good evidence.

Of course, the study data is analyzed using standard statistical tests for probability or for statistical significance. When results comparing the controlled group with the experimental group are analyzed, one looks to see if the differences between groups are statistically significant (less risk that differences are from chance alone) and if the probability ratio is high. There is not a specific number regarding what probability number (such as an odds ratio, risk ratio, hazard ratio, etc.) is considered to be high, but I have seen information reporting a study with an odds ratio less than 3 is not a strong value.

The confidence interval (CI) must also be examined. When a wide CI is reported, the data is scattered widely and the results are less reliable, with the true probability for risk close to the lower limit of the CI.

Slim: Why are so many dental speakers/writers/professionals promoting this link now that we know the relationship is not causal?

Pickett: Well, we clearly know that periodontal treatment will not reduce adverse pregnancy outcomes. The Srinivas et al. cohort study indicates that the previous reports of an association between PD and APO may be spurious. Some people still call for more studies suggesting there is a relationship, but the specific factors are unclear at this time.

My question is “What biologic plausibility will be studied, since studies must relate to a realistic biologic plausibility for the relationship?”

I cannot think of any reason for a speaker to suggest there is a true relationship suggesting that periodontal infection leads to APOs. Certainly studies with bias should not be used to support this claim. Speakers are expected to present nonbiased, nonjudgmental presentations, which do not mislead participants and which do not contain deceptive information.

Slim: Based on the evidence to date, what should the dental hygienist say to a pregnant patient who presents with periodontal disease?

Pickett: The oral health-care professional is a scientist and should use the best science, nonbiased studies, and adequately powered studies to guide participants in a course. It is clear that receiving periodontal treatment is safe during pregnancy. It is clear that good plaque control can reduce gingival bleeding (whether one is pregnant or not) and it is accepted that regular oral examination and indicated care is a practice that will help prevent periodontal problems.

In addition, information regarding how to care for an infant’s oral cavity is important, along with teaching a mother how to identify dental decay in a child’s teeth, and encouraging parents to take the child to a dentist for an oral exam at six months of age.

The FDA recently announced that research has shown no health effects from receiving amalgam fillings in pregnant women. However, mercury can cross the placenta. In general, pregnant women are advised to consult with a dentist regarding options for dental restorations. Because of the limited amount of evidence regarding safety, women should probably not get amalgam fillings during pregnancy. Dentists can suggest other materials for any pregnant woman who needs a restoration.6 This is what I would tell patients under my care.


1. Offenbacher S, Katz V, Fertik G, Collins J, Boyd D, Maynor G, et al. Periodontal infection as a possible risk factor for preterm low birth weight. Journal of Periodontology 1996;67(10 Suppl):1103-13.
2. Jeffcoat MK, Hauth JC, et al. Periodontal disease and preterm birth: results of a pilot intervention study. J Periodontol 2003;74(8):1214-18.
3. Uppal A, Uppal S, Pinto A, et al. The effectiveness of periodontal disease treatment during pregnancy in reducing the risk of experiencing preterm birth and low birth weight. A meta-analysis. J Am Dent Assoc 2010;141:1423-34.
4. Polyzos NP, Polyzos IP, Zavos A, et al. Obstetric outcomes after treatment of periodontal disease during pregnancy: Systematic review and meta-analysis. BMJ, 2010;341:c7017.
5. Srinivas SK, Sammel MD, Stamilio DM, Clothier B, Jeffcoat MK, Parry S, et al. Periodontal disease and adverse pregnancy outcomes: is there an association? American Journal of Obstetrics & Gynecology 2009;200(5):497.e1-8.
6. U.S. Food and Drug Administration. (2009). Class II special controls guidance document: Dental amalgam, mercury, and amalgam alloy-guidance for industry and FDA staff. Retrieved from

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