This blinded randomised clinical study proceeded in three
phases: (1) determination of the minimum severity of periodontal
disease required to be included in the study and
randomised for treatment; (2) an overall treatment intervention;
and (3) intervention analysis based on the efficacy
of the periodontal treatment. Figure 1 shows the patient
and information flow of the study as a whole. The primary
outcome was the incidence of spontaneous preterm births
before 35 weeks of gestation.