Studies on the link between periodontal disease and preterm birth have produced conflicting results. Although some show that women with gum disease are more likely to deliver a baby before term — which sets up the baby for health risks — others have not found a link. Studies are ongoing.
Despite those conflicting results, other research has found that treating periodontal disease in pregnant women helps them carry their infants to term. In a recent study, researchers found that women with periodontal disease who completed periodontal treatment before the 35th week were less likely to deliver their babies before term than those with periodontal disease who did not get treatment.
Source: http://www.webmd.com/