Background. CenteringPregnancy (CP) is a multifaceted group based care-model integrated in routine prenatal care, combining health assessment, education, and support. CP has shown some positive results on perinatal outcomes. However, the effects are less obvious when limited to the results of randomized controlled trials: as there are few trials and there is a variation in reported outcomes. Furthermore, former research was mostly conducted in the United States of America and in specific (often high risk) populations. Our study aims to evaluate the effects of CP in the Netherlands in a general population of pregnant women (low and high risk). Furthermore we aim to explore the mechanisms leading to the eventual effects by measuring potential mediating factors. Design. We will perform a stepped wedge cluster randomized controlled trial, in a Western region in the Netherlands. Inclusion criteria are <24 weeks of gestation and able to communicate in Dutch (with assistance). Women in the control period will receive individual care, women in the intervention period (starting at the randomized time-point) will be offered the choice between individual care or CP. Primary outcomes are maternal and neonatal morbidity, retrieved from a national routine database. Secondary outcomes are health behavior, psychosocial outcomes, satisfaction, health care utilization and process outcomes, collected through self-administered questionnaires, group-evaluations and individual interviews. We will conduct intention-to-treat analyses. Also a per protocol analysis will be performed comparing the three subgroups: control group, CP-participants and non-CP-participants, using multilevel techniques to account for clustering effects. Discussion. This study contributes to the evidence regarding the effect of CP and gives a first indication of the effect and implementation of CP in both low and high-risk pregnancies in a high-income Western society other than the USA. Also, measuring factors that are hypothesized to mediate the effect of CP will enable to explain the mechanisms that lead to effects on maternal and neonatal outcomes. Trial registration. Dutch Trial Register, NTR4178, registered September 17th 2013.