AimTo describe factors associated with women's knowledge of nutrition, knowledge of nutrient supplements and use of supplements that are routinely recommended during preconception and pregnancy.MethodsParticipants (women 18–45 years, pregnant or planning pregnancy) were recruited from a consumer survey panel and completed an online, custom‐built questionnaire. Responses were used to calculate individual scores for nutrition knowledge (range 0–30) and supplements knowledge (range 0–10), where higher scores indicated better knowledge, and determine use of routinely recommended supplements (yes/no). Statistical tests of independence were used to explore associations between these outcomes and 68 variables derived from the survey.ResultsOf 2289 respondents, 776 were eligible and 624 (80.4%) completed the survey. Among pregnant women (N = 144) and those planning a pregnancy (N = 480), nutrition knowledge and supplements knowledge was limited, and daily use of routinely recommended supplements was low (63.5% pregnant, 40.1% planners). The odds of appropriate supplement use was strongly associated with health literacy adequacy. There was a low positive correlation between supplements beliefs and nutrition/supplements knowledge. Nutrition and supplements knowledge was associated with information provided by a wider number of health and allied health services during preconception than during pregnancy.ConclusionHealthcare providers are central to preconception and pregnancy dietary and nutrient supplement advice. Our data reinforce the role of adequate health literacy in applying this advice and suggest that an understanding of women's beliefs about supplements and targeting the source of the information to women at different stages (preconception or pregnant), could be used to better tailor these communications.