The World Drug Report 2019 presented an alarming figure to the world: more than 5% of the world's population has been using some type of illicit drug, and that number is growing every year. While its use increases, its abuse during pregnancy has become a global public health problem, resulting in medical and social challenges related to maternal and child health. In this context, the objective of this review was to determine the prevalence of illicit drug use during gestation across the globe, alongside with a critical review of the evaluated studies. Research was performed by simultaneously searching terms ("pregnant woman OR pregnant" OR "gestation" OR "pregnancy" AND "illicit drugs" OR "street drugs") in the databases of the Scientific Electronic Library Online, PubMed, and Web of Science. Comparisons between studies were performed in software Statistica 10.0. The data presented worrying results in relation to the variation in prevalence of illicit drug use during pregnancy, when comparing studies based on interviews or questionnaires (self-reported) (1.65%) and studies based on toxicological analysis (12.28%). In addition, we emphasize the high prevalence (5.16%) of illicit drug use among adolescent pregnant women and the low number of studies on this population. This study reveals worrying data about pregnant drug-user population, mainly the underestimation of prevalence in studies that use only questionnaires or similar methods in comparison to studies that use toxicological analysis of biological matrices. This scenario reveals necessity for health systems in different countries to establish specific public health policies for this population.