Oral Health’s Involvement in Adverse Birth Outcomes

Optimal oral health is critical to the overall health of pregnant women and their babies. Untreated maternal oral conditions can be a major risk factor for health complications in the developing fetus or newborn.^1,2 Unfortunately, oral health is often overlooked in the scope of comprehensive prenatal care.³ For example, only 22% to 34% of women in the United States seek treatment or preventive care from a dentist during pregnancy.^3,4

Maternal periodontal disease has been associated with preterm birth, development of preeclampsia and gestational diabetes, and delivery of low-birth weight (LBW) infants. The transfer of maternal oral bacteria to newborns may also predispose them to caries.^4,5 Both periodontal disease and caries are highly prevalent in women of child-bearing age, particularly among low-income women and members of certain racial and ethnic groups.^4,5 Eke et al⁶ report that 38.4% of American women age 30 and older have some form of periodontal disease, with 65.4% of these individuals living below the federal poverty level. A recent study identified a 73.9% prevalence of periodontal disease among women ages 18 to 40.⁷ In 2012, 25.9% of women between the ages of 20 and 44 had untreated caries, an increase of 4.1% since 2008; among these, 41.4% were African American and 35.7% were Hispanic.⁸ Consequently, oral health professionals and prenatal providers need to emphasize the importance of receiving professional oral health care during pregnancy and educate pregnant women about oral disease prevention.^{1,2,4,5,9–13}

Since 2000, research has identified the presence of multiple oral bacterial species in locations outside of the oral cavity. Streptococcus mutans (brain abscess), Aggregatibacter actinomycetemcomitans (bacterial endocarditis) and A. actinomycetemcomitans and Porphyromonas gingivalis (atherosclerotic plaques in the aorta) have all been discovered throughout the body, substantiating the relationship between oral and systemic health.¹³ Preterm birth, LBW infants and periodontal disease all have biological, social and behavioral determinants that can increase the likelihood of occurrence.^2,14 Studying the direct effect of any one risk factor on the outcomes of preterm birth and LBW babies is challenging due to the many confounding variables that may generate the same outcome.¹⁴ However, it is clear that the status of a patient’s oral ­condition affects the individual’s systemic health — and possibly the success of a pregnancy and health of the infant.

ADVERSE BIRTH OUTCOMES

Preterm birth and LBW are major causes of infant mortality and morbidity — and, despite numerous attempts by multiple public health entities to reduce their prevalence, they continue to be a significant public health issue.^15–18 In 2012, 450,000 babies were born preterm in the United States, accounting for 35% of all infant deaths.¹⁹ In 2015, 8% of all infants born in America were LBW. The prevalence of LBW is higher among non-Hispanic black infants (13.2%) and Puerto Rican infants (9.5%) than among infants of any other racial or ethnic group.⁸ The World Health Organization estimates that 15 million babies are born preterm every year around the globe. This adverse birth outcome is the leading cause of death among children younger than 5.²⁰ Approximately seven out of 10 LBW babies are born prematurely.²¹ Preterm birth refers to infants born before 37 weeks of gestation,¹⁹ while LBW is defined as birth weight less than 2500 grams (5.5 pounds).²¹

The gestational age of infants is the most important predictor of their subsequent health and survival.²² Premature infants have a greater risk of feeding difficulties, respiratory distress and delayed brain development, as well as lifelong health complications, such as vision problems, developmental delays, deafness and poor motor skills.^{2,4,5,17,22–24} Babies born at a LBW may be more likely than infants born at a normal weight to develop certain health conditions later in life, including diabetes, heart disease and high blood pressure.²¹

There are multiple causes for adverse pregnancy outcomes. In many cases, preterm births can be attributed to infection or other chronic systemic conditions (diabetes and/or high blood pressure).²⁰ In approximately 50% of preterm births, however, the direct cause is not immediately known.¹³ Some factors that may cause preterm birth include a history of premature births, chronic health conditions (e.g., high blood pressure, preeclampsia or diabetes), insufficient maternal weight gain during pregnancy, smoking, alcohol consumption, use of illegal drugs/abuse of prescription drugs, stress and belonging to a certain racial/ethnic group (e.g., African-American).^13,25–27

The high prevalence of preterm births and LBW infants emphasizes the need to reduce or eliminate risk factors that may contribute to their occurrence. This includes acknowledging the possible relationship of these adverse pregnancy outcomes with untreated maternal periodontal disease and incorporating oral health practice guidelines into routine obstetrical care.

MECHANISM OF PERIODONTITIS

During pregnancy, changes in hormone levels promote an inflammatory response that increases the risk of developing gingivitis and periodontitis.^5,13 Pregnancy-induced gingivitis — the most common oral disease in pregnancy — may manifest as gingival inflammation, erythema and bleeding (spontaneous or after manipulation).¹ The majority of pregnant women may experience gingivitis due to pregnancy-related hormonal changes.^3,13,28 Studies have identified a large range regarding the prevalence of pregnancy gingivitis, from 36% in one study to 100% in another.^3,13,28 Differences in study design and demographics of study participants may account for these considerable variations.

The destructive process of periodontitis involves both direct tissue damage resulting from the presence of bacteria surrounding the teeth and their adjacent structures, as well as indirect damage caused by the host’s inflammatory response.^{13,15,17,29,30} The systemic inflammation caused by periodontal infection and bacterial colonization in the oral cavity may play a role in adverse pregnancy outcomes.³¹ Researchers hypothesize that periodontal pathogens (inflammatory mediators) reach the maternal reproductive system through the bloodstream and cause an inflammatory cascade, triggering a second round of inflammatory responses.^{13–15,29,31–33} Eventually, the bacteria, virulence factors and inflammatory cytokines reach the placenta and create a new bacterial infection, initiating an inflammatory response at the fetal/placental interface.^13,30,34,35 As more inflammatory cytokines are produced, tissue destruction can occur, affecting the structural integrity of the placenta.^13,30,32,35 Related to the onset of labor, these cytokines induce tenderness of the uterine muscles, stimulate uterine contractions and cervical dilation, and trigger preterm birth.^13,30,35

In some cases of preterm birth, elevated levels of these cytokines have been found in the amniotic fluid.³⁰ One study discovered P. gingivalis, a pa­thogen observed in periodontitis, in the amniotic fluid of women with threatened premature labor.³⁶ Researchers found that the P. gingivalis antigens were numerous in the placental tissues, strengthening the theory of bacterial migration from the oral cavity to the fetus.³⁶ Other studies have successfully isolated the anaerobic microbe Fusobacterium nucleatum from the amniotic fluid, placenta and chorio-amnionic membranes of women delivering premature­ly.^{14,31,35–40} Another study identified P. gingivalis and A. actinomycetemcomitans in the amniotic fluid of women with active periodontitis.¹⁴ Studies have discovered a statistically significant relationship be­tween the presence of active maternal periodontal disease and premature birth and/or LBW.^{2,18,28,41–45}

In 2016, Corbella et al¹⁵ published a systematic review that measured the potential association between adverse birth outcomes and periodontitis. The authors examined and analyzed case-control and prospective cohort studies (n=22). Upon investigating the studies’ characteristics (including total number of subjects, mean age of subjects, and definition of periodontal disease), control of possible confounders, and risk of bias, the researchers concluded that periodontitis may be a risk factor for preterm birth, LBW, and preterm LBW — although the association was low. The authors concluded that while a low association between periodontitis and adverse birth outcomes had been identified, additional research is needed to establish a more definitive causal relationship, as well as to measure the effect of nonsurgical periodontal therapy and a reduction in adverse birth outcomes.¹⁵

Other studies and systematic reviews have revealed contradictory results.^{16,44,46–50} Vettore et al⁵⁰ performed a case-control study among postpartum women (n=542) to compare periodontal health with birth outcomes. They concluded periodontal disease did not increase the risk of preterm LBW, according to 15 measures of periodontal disease. Another study also assessed whether the presence of periodontitis impacted adverse birth outcomes.⁵¹ Researchers conducted a prospective cohort study on pregnant women (n=73) who were between 28 weeks and 36 weeks gestation. Among this study population, periodontitis was not shown to be a risk factor for preterm delivery or a LBW infant.⁵¹ Probable reasons for these discrepancies could be the differences in study definitions and methods of diagnosis for preterm birth, preterm LBW or periodontitis, as well as disparities in confounder controls, study participant numbers and demographics.^13,17

Studies performed on the effect of nonsurgical treatment of periodontitis in pregnant women and its impact on reducing rates of preterm births or LBW infants have produced different results. Fiorini et al⁵² and Kaur et al⁵³ documented that while periodontal treatment improved clinical oral conditions and decreased inflammatory markers, there was no significant decrease in the incidence of adverse birth outcomes. Other studies have found a reduced prevalence of preterm births after treating severe periodontitis in pregnant women.^13,54–57 However, studies performed by Xiong et al,⁵⁸ Horton et al⁵⁹ and Han⁶⁰ observed no positive effect of periodontal treatment on reducing adverse birth outcomes. Similar to the lack of definitive research concerning the causal relationship between periodontitis and preterm births/LBW infants, researchers hypothesize that these conflicting data are due to the inconsistent study definitions used to classify disease, and the possible lack of control for other factors, such as smoking, maternal age and ethnicity.¹³

ORAL HEALTH CARE DURING PREGNANCY

In 2012, the National Maternal and Child Oral Health Resource Center published Oral Health Care During Pregnancy: A National Consensus Statement. This report, in addition to statements by the American Academy of Periodontology and American College of Obstetricians and Gynecologists, documents the necessity and importance of maintaining maternal oral health during pregnancy, as well as promoting a collaborative effort between prenatal providers and oral health practitioners to provide oral health education, preventive care and dental treatment during the gestational period.^61,61–64

Most importantly, these consensus statements aim to reassure the safety of preventive care and therapeutic treatment during pregnancy. Radiographic exposures (with proper shielding of the thyroid and abdomen) for diagnostic procedures do not pose any risk to the developing embryo or fetus, and are considered safe throughout the entire pregnancy.^12,62 Routine prophylaxis, scaling and root planing, restorative procedures and local anesthesia are also considered safe, and may be performed on women at any time during pregnancy.^{12,62­­–64}

NECESSITY OF FUTURE RESEARCH

This literature review indicates that periodontitis is an oral disease that may have an adverse effect on birth outcomes, including preterm births and LBW infants. Although there is inconclusive research relating to the treatment of periodontitis and its effect on improving birth outcomes, maintaining oral health during pregnancy significantly decreases the maternal bacterial load in the oral cavity, improving overall health.¹³ In addition, while the link between oral pathogens and systemic health has been documented,^{13,14,31,35–40,65} there is still further need to definitively link periodontal disease with adverse birth outcomes in order to more successfully manage chronic disease and promote maternal and child health.

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From Decisions in Dentistry. November 2017;3(11):31–34.