All periodontal treatment is conducted in the Oral Health Centre of Western Australia (OHCWA), located 2 km from KEMH. A full periodontal examination is first performed using a constant force automated Florida probe (Florida Probe Corporation, Gainesville, Florida, USA) which provides precise measurements of pocket depth to 0.2mm, and stores data directly into a computer. This measurement system has been used in our pilot study and two separate probes and computer systems are available for this trial. Further periodontal parameters are recorded, including clinical attachment loss, full mouth bleeding after probing, and modified O’Leary Plaque Index. Treatment explanation is then provided by the hygienist and consent confirmed. The treatment plan for each woman is determined in consultation with a study periodontist and is conducted over 3 visits each of one hour duration. These treatments consist of non-surgical debridement of the sub- and supra-gingival plaque, removal of local predisposing factors such as calculus, and adjustment of overhanging restorations. Comprehensive oral hygiene instruction and motivation is provided at each visit as required. This oral hygiene advice recommends tooth brushing and flossing after every meal and rinsing with 0.12% non-alcohol based chlorhexidine mouth wash. These treatments are provided on 3 occasions at weekly intervals commencing at 20 weeks gestation.