Women are ineligible if they are: unable to attend for periodontal treatment; less than 16 years of age; present for antenatal care after 20 weeks gestation; are unable to understand the implications of participation in the trial; have a fetus with a known abnormality that would predispose the pregnancy to pre-term birth such as those that may cause polyhydramnios; have a multiple pregnancy; have cardiac disease that would require antibiotic therapy for dental treatment; are currently receiving periodontal treatment; or have fewer than 20 teeth.