Pregnancy and lactation represent a complex stage from a nutritional point of view, since energy, protein and micronutrient requirements increase during these stages. The literature describes that a well-planned plant-based diet can be sufficient in energy, macronutrients and micronutrients, with the exception of vitamin B12 and possibly n3 polyunsaturated fatty acids, mainly EPA and DHA. During the last few years, adherence to this diet has increased rapidly in the population, so the main objective of this article is to review the current evidence on the intake and concentrations of vitamin B12, EPA and DHA during pregnancy and lactation in women following a plant-based diet. A literature search was performed in PubMed, Scopus, Web of Science and Ovid MedLine using free terms and MESH. Eleven articles were selected in this review. Well-planned vegetarian and vegan diets, with adequate supplementation of vitamin B12, EPA and DHA, are compatible during pregnancy and lactation, being a positive predictor of their content in breast milk. A similar situation was observed in plasma levels in women supplemented with B12. However, it is important to continue with research in this area that considers an adequate dietary anamnesis, integral evaluation of nutritional status, estimation of nutritional requirements and an individualized nutritional plan.