OBJECTIVE To determine pregnant women's knowledge of and adherence to the recommendations for periconceptional folic acid supplementation (PFS) and iodine supplementation (IS). Secondary objectives include determining predictors of adherence, and identifying influential nutrition information sources. METHODS A cross-sectional online survey was completed by 857 pregnant women, including a national cohort (n=455) recruited using an online panel provider and a South Australian cohort (n=402) recruited from a public maternity hospital. RESULTS Adherence to PFS and IS recommendations was 27% and 23%, respectively. Planning pregnancy and awareness of the correct timing of recommendations were predictors of adherence for both recommendations. Not consuming any alcohol during pregnancy and living in metropolitan areas also predicted adherence to the IS recommendation. Awareness of the recommendation was greater for folic acid (more than 90%) than iodine (56-69%). Knowledge of the importance of folic acid and iodine was greater than knowledge regarding the recommended dose and timing of supplementation. Main healthcare providers were considered the most influential nutrition information sources. CONCLUSIONS AND IMPLICATIONS Knowledge of and adherence to supplement recommendations for preconception and pregnancy needs improvement. While main healthcare providers may play an important role, further research is needed to explore strategies for increasing adoption of recommendations.