Carter 1989.

Methods	Cluster‐randomized trial. Unit of randomization was the antenatal class.
Participants	432 pregnant women attending 52 prenatal classes offered for free by a public health agency in Ontario. Completed both the pre‐test and the post‐test questionnaire 285 women (122 in the experimental arm and 163 in the control arm). Loss to follow‐up was 34%.
Interventions	10‐minute teaching session during the first prenatal class on how to avoid toxoplasmosis infection.
Outcomes	Pet hygiene behavior of cat owners. Food hygiene behaviors. Personal hygiene behaviors.
Notes	A behavior change scoring system was developed: a woman gained 1 point for every change toward a useful behavior, while she lost 1 point for every change toward a dangerous behavior. The authors did not report raw data (number or proportion): only the significance test data (P value) for differences were reported. We have contacted the authors for the original data but have not yet received a reply.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described in the publication.
Allocation concealment (selection bias)	Low risk	Not described in the publication. However, as all the centers present in that jurisdictional area were involved, an equal number of classes in each center received the experimental and the control intervention, and this is a cluster‐randomized trial, thus the units of randomization are the prenatal groups, the lack of allocation concealment is unlikely to influence the outcome.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Blinding of the women reported, blinding of the personnel was not possible, but unlikely to influence the outcome.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Measure of knowledge and behavior were self‐reported.
Incomplete outcome data (attrition bias) All outcomes	High risk	Losses to follow‐up were 34% (432 women completed the pretest questionnaire and 285 completed the post‐test questionnaire): women in experimental group were more likely to be lost at follow‐up than women in control group.
Selective reporting (reporting bias)	Unclear risk	All of the pre‐specified outcomes have been reported. However, the study did not report seroconversion rate during pregnancy, which is an outcome of interest.
Other bias	Unclear risk	Contamination between groups can not be excluded.