Purpose : Most industrialized countries have introduced maternity protection legislation (MPL) to protect the health of pregnant workers and their unborn children from workplace exposure. This review aimed to assess this legislation’s level of implementation, barriers and facilitators to it, and its expected or unexpected effects. Methods : A realist narrative review was conducted. Keyword searches of the PubMed, CINAHL, PsycINFO, MIDIRS, Sociological abstracts and Google Scholar electronic databases were performed in March 2018. Results : The 42 publications included show that the implementation of MPL is deficient in most countries. Allowing pregnant women to withdraw from work on preventive leave or sick leave is favored over workplace adaptations or worker reassignments. The publications highlight mechanisms which encourage or obstruct the enforcement of legislation at the levels of the individual, the physical and social environment, and the macrosocial context. The delay between the conception and implementation of maternity protection measures appears to be a major barrier to the efficacy of MPL. The literature also suggests that unexpected adverse effects, such as degradation in working relationships or discrimination can obstruct the implementation of protective measures. Conclusions : This study showed the need for a better implementation of MPL during pregnancy. Further research and recommendations for improvements in MPL should consider the diverse mechanisms and effects of its implementation. Barriers and adverse effects of this implementation do not only ensure a lack of information or awareness about MPL, but are also linked to contradictions between requirements to protect employment and protect pregnancy.