Background Unhealthy prenatal lifestyle behaviours are associated with adverse pregnancy outcomes, but little is known about what motivates women to comply with preconceptional lifestyle recommendations or consciously plan their pregnancy. Therefore, the objective of this study is to explore the associations between preconceptional lifestyle behaviours, health beliefs and pregnancy planning among Dutch pregnant women. Methods In this cross-sectional study based on the data of the APROPOS-II study, 1,077 low-risk pregnant women were eligible for inclusion. Preconception lifestyle behaviours and actively preparing for pregnancy were assessed in relation to planned pregnancies (based on the London Measure of Unplanned Pregnancies) and health beliefs (14 statements). The following preconceptional lifestyle behaviours were assessed through a self-administered questionnaire in the first trimester of pregnancy: fruit intake, vegetable intake, caffeine intake, (second-hand)smoking, alcohol intake, folic acid supplement use and exercise. Data were analysed using multivariate logistic regression analyses. Results A total of 921 (85.5%) women in our cohort had a planned pregnancy. However, of these women, 640 (69.5%) adequately used folic acid supplements and 465 (50.5%) women consumed alcohol at any point during pregnancy. Of the women considering themselves ‘healthy enough and not needing preconception care’, 48 (9.1%) women had an adequate vegetable intake, 294 (55.6%) women consumed alcohol at any point during pregnancy and 161 (30.4%) women were either over-or underweight. Conclusion Despite consciously planning their pregnancy, most women did not adhere to preconceptional lifestyle behaviour recommendations. Women’s health beliefs and overestimation of their health status seem to interfere with actively planning and preparing for pregnancy. Findings from our study may encourage the development of prospective health-promoting interventions that focus on health beliefs and actively preparing for pregnancy, to improve preconceptional lifestyle behaviours, thereby optimizing the health of future generations.