But in a newly reported study -- one of the largest ever to examine the question -- deep cleaning and plaque removal during pregnancy was found to have no impact on early birth outcomes.
The study, which included 1,800 pregnant women with periodontal disease, was presented today in San Diego at the 29th annual meeting of the Society for Maternal-Fetal Medicine.
Similar findings were reported in a separate trial involving 823 women; those findings were published in the New England Journal of Medicine in late 2006.
Both studies compared outcomes among women with periodontal disease who did and did not receive routine tooth and gum treatment during pregnancy.
"I think it is pretty clear that the type of treatment used in these studies does not reduce the risk of premature delivery," ob-gyn professor Robert L. Goldenberg, MD, of Philadelphia's Drexel University, tells WebMD.
Gum Disease and Preterm Birth
But it is still not clear if more aggressive treatment of periodontal disease affects risk or if treating tooth and gum issues before a woman becomes pregnant can help prevent premature delivery, Steven Offenbacher, DDS, PhD, of the University of North Carolina, Chapel Hill's Center for Oral and Systemic Diseases, tells WebMD.
Offenbacher was the lead investigator of the newly reported study, which was conducted at UNC, Duke University Medical Center, the University of Alabama at Birmingham, and the University of Texas at San Antonio.
All of the pregnant women recruited for the study had periodontal disease. Half were treated with deep cleaning and plaque removal before reaching their 23rd week of pregnancy and the other half received no treatment while pregnant.
The two groups were followed through delivery. After controlling for well-known risk factors for early delivery, such as smoking and history of giving birth prematurely, the researchers found no significant difference in birth outcomes among the two groups.
About a quarter of women with periodontal problems experience a worsening of tooth and gum issues during pregnancy, but the reasons for this are not clear, Offenbacher says.
"This study shows that this level of periodontal treatment does not affect birth outcomes, but we don't know if more intensive treatment can make a difference," he tells WebMD.
Many Questions Remain
Study co-author Amy Murtha, MD, says there is still much that is not known about the relationship between poor oral hygiene and early delivery.
Murtha is director of obstetrics research at Duke University Medical Center.
"Periodontal disease and poor pregnancy outcomes travel together, but we don't know why," she says in a new release.
Goldenberg, who was not involved in the study, says future research should focus on oral hygiene prior to pregnancy.
"It is pretty clear that there is some association between periodontal disease and preterm birth, but we can't say that this is a cause-and-effect relationship," he says.