Background: Parents' thoughts about childbirth during pregnancy are important for the adjustment process but little is known about factors associated with such thoughts. Objectives: To describe and study background characteristics, feelings and support in relation to thoughts about childbirth in mid-pregnancy, in women and their partners and to analyze which factors are most important for having thoughts and feelings about childbirth. Method: A cross-sectional study of 1212 women and 1105 men recruited shortly after the routine ultra sound examination in pregnancy weeks 17-19. Data was collected by a questionnaire in mid-pregnancy. Data were analyzed using relative risks with 95% confidence interval and logistic regression. Results: A high proportion of women (75%) and men (67%) reported having thoughts about childbirth. In women childbirth related fear Odds Ratio (OR) 2.7; [95% CI 1.62-4.37], high level of education (OR 1.8, [95% CI 1.32-2.34] and major emotional changes OR 1.5, [95% CI 1.0-2.1] were the most important factors associated with having thoughts about childbirth. In men, high level of education OR 1.1 [95% CI 1.41-2.52], getting the opportunity to ask question at prenatal visits OR 1.6 [95% CI 1.17-2.07], and expecting the first baby OR 1.6 [1.17-2.07] contributed most to the model. Discussion: This study shows that the majority of prospective parents think about the birth of their baby in mid-pregnancy. Some factors are common for both parents, but women's thoughts are more based on emotional and physical changes and fears while men's are more based on the social situation such as expecting the first baby and organizational issues in prenatal care, and instrumental issues such as finances. Further studies are needed about the content of the parents' thoughts.