Simple Summary: In the last few years, several clinical trials have evaluated the potential positive effects of probiotics supplementation against several adverse pregnancy outcomes. However, it is currently questionable whether the existing studies are adequate to derive potential recommendations of high validity and accuracy. From this perspective, the aim of the current narrative review focuses on the critical summarization and scrutinization of the currently available clinical studies by searching the most precise international databases, such as PubMed, Scopus, and Web of Sciences. Most of the existing evidence seems promising, rendering probiotics as potential effective preventive factors and/or co-treatment agents against diverse adverse pregnancy outcomes. However, there are several limitations and high heterogeneity amongst the existing clinical studies to be considered in order to derive specific recommendations of high validity to introduce probiotics supplementation in the clinical practice. Thus, further research is highly recommended in order to obtain more adequate conclusions. Background: Probiotics, as supplements or food ingredients, are considered to exert promising healthy effects when administered in adequate quantity. Probiotics' healthy effects are related with the prevention of many diseases, as well as decreasing symptom severity. Currently, the most available data concerning their potential health effects are associated with metabolic disorders, including gestational diabetes mellitus. There is also clinical evidence supporting that they may exert beneficial effects against diverse adverse pregnancy outcomes. The purpose of the current narrative study is to extensively review and analyze the current existing clinical studies concerning the probable positive impacts of probiotics supplementation during pregnancy as a protective agent against adverse pregnancy outcomes beyond gestational diabetes mellitus. Methods: a comprehensive and thorough literature search was conducted in the most precise scientific databases, such as PubMed, Scopus, and Web of Sciences, utilizing efficient, representative, and appropriate keywords. Results: in the last few years, recent research has been conducted concerning the potential beneficial effects against several adverse pregnancy outcomes such as lipid metabolism dysregulation, gestational hypertensive disorders, preterm birth, excessive gestational weight gain, caesarean risk section, vaginal microbiota impairment, mental health disturbances, and others. Conclusion: up to the present day, there is only preliminary clinical data and not conclusive results for probiotics' healthy effects during pregnancy, and it remains questionable whether they could be used as supplementary treatment against adverse pregnancy outcomes beyond gestational diabetes mellitus. [ABSTRACT FROM AUTHOR]