Purpose: As more newborns have received expanded newborn screening (NBS) for metabolic disorders, the overall number of false-positive results has increased. The purpose of this study was to explore the nature of the psychological impacts experienced by mothers related to the NBS process. Methods: An online parenting community in Korea was selected, and questions regarding NBS were collected using web crawling for the period from October 2018 to August 2021. In total, 634 posts were analyzed. The collected unstructured text data were preprocessed, and keyword analysis, topic modeling, and visualization were performed. Results: Of 1,057 words extracted from posts, the top keyword based on ‘term frequency-inverse document frequency’ values was “hypothyroidism,” followed by “discharge,” “close examination,” “thyroid-stimulating hormone levels,” and “jaundice.” The top keyword based on the simple frequency of appearance was “XXX hospital,” followed by “close examination,” “discharge,” “breastfeeding,” “hypothyroidism,” and “professor.” As a result of LDA topic modeling, posts related to inborn errors of metabolism (IEMs) were classified into four main themes: “confirmatory tests of IEMs,” “mother and newborn with thyroid function problems,” “retests of IEMs,” and “feeding related to IEMs.” Mothers experienced substantial frustration, stress, and anxiety when they received positive NBS results. Conclusion: The online parenting community played an important role in acquiring and sharing information, as well as psychological support related to NBS in newborn mothers. Nurses can use this study’s findings to develop timely and evidence-based information for parents whose children receive positive NBS results to reduce the negative psychological impact.