The relation between oral microbes of mother and child encompasses several aspects. It has been shown that a bad periodontal condition is a risk factor for low birth weight. The bacterium that is most specifically associated with dental caries, Streptococcus mutans, can be transmitted between mother and child; it has been suggested that the age of colonization with this bacterium is a risk factor for caries in the child. Also periodontal bacteria can be transmitted between mother and child. It remains to be elucidated whether this is an additional risk factor for the development of periodontal disease.