Problem: Despite the introduction of preventive guidelines, no decrease in the incidence of early onset infection was observed. Background: Early onset group B streptococcal (EOGBS) infection is an important cause of neonatal morbidity and mortality. Aim: Our study was conducted to determine adherence to three guideline-based group B streptococcus (GBS) preventive strategies. Methods: A prospective experimental study clustered by obstetric collaboration region was performed between March 2013 and August 2014 among midwives, obstetricians and paediatricians in the Netherlands. At baseline, the three regions operated according to the Dutch preventive strategy (founded on the risk-based strategy) in order to prevent EOGBS infection, whereas in the study period they followed either the risk-based, the combination or the Dutch strategy. Adherence was measured prospectively per pregnant woman, using predefined core elements of each preventive strategy: identification of risk factors, maternal GBS screening, application of intrapartum antibiotic prophylaxis and observation of the child. Data about adherence to the core elements were collected from medical records, maternal questionnaires and laboratory test results. Findings: In the three regions, a total of 121 care providers and 1562 women participated. We found an overall adherence of 90% to the risk-based strategy, 57% to the combination strategy and 89% to the Dutch strategy. Adherence to a strategy in case women had EOGBS risk factors was below 20% in all strategies. Discussion: The majority of women with EOGBS risk factors did not receive the care prescribed by any of three preventive strategies and were not treated optimally. Conclusion: The risk-based and the Dutch strategy are the recommended strategies for implementation.