Background: In 2015, a quality improvement project called "Adequate Childbirth Project" (PPA) was implemented in Brazilian private hospitals in order to reduce cesarean sections without clinical indication. The PPA is structured in four components, one of which is directed at women and families. The objective of this study is to evaluate the effects of PPA on women's preference for vaginal birth (VB) at the end of pregnancy. Methods: Evaluative research conducted in 12 private hospitals participating in the PPA. Interviews were carried out in the immediate postpartum period and medical record data were collected at hospital discharge. The implementation of PPA activities and women's preference for type of birth at the beginning and end of pregnancy were compared in women assisted in the PPA model of care and in the standard of care model, using a chi-square statistical test. To estimate the effect of PPA on women's preference for VB at the end of pregnancy, multiple logistic regression was performed with selection of variables using a causal diagram. Results: Four thousand seven hundred ninety-eight women were interviewed. The implementation of the planned activities of PPA was less than 50%, but were significantly more frequent among women assisted in the PPA model of care. Women in this group also showed a greater preference for VB at the beginning and end of pregnancy. The PPA showed an association with greater preference for VB at the end of pregnancy in primiparous (OR 2.54 95% CI 1.99-3.24) and multiparous women (OR 1.44 95% CI 0.97-2.12), although in multiparous this association was not significant. The main factor associated with the preference for VB at the end of pregnancy was the preference for this type of birth at the beginning of pregnancy, both in primiparous (OR 18.67 95% CI 14.22-24.50) and in multiparous women (OR 53.11 95% CI 37.31-75.60). Conclusions: The PPA had a positive effect on women's preference for VB at the end of pregnancy. It is plausible that more intense effects are observed with the expansion of the implementation of the planned activities. Special attention should be given to information on the benefits of VB in early pregnancy.