BACKGROUND AND OBJECTIVE: Medication use is increasing to treat both pre-existing and pregnancy-related medical conditions or complications. This study aims to investigate factors associated with multiple medication use during pregnancy, as well as any increased risk of pregnancy complications for women taking multiple medications. METHODS: A retrospective analysis of routinely collected medical records of singleton pregnant women was conducted in Southeast Melbourne, Australia, between 2016 and 2021. Self-reported medication use was recorded as part of routine medical care, starting from the first antenatal booking appointment and continuing for every subsequent antenatal appointment until birth. Multimorbidity was defined as having two or more medical conditions. Logistic regression was used to assess factors influencing multiple medication use (defined as taking two or more non-supplemental medications at any stage of pregnancy) and associations with pregnancy complications. RESULTS: Of 48,502 participants, 34.9% used one medication, while 11.7% used multiple medications. Women of older age (30-34, 35-39, and ≥ 40 years), higher body mass index (25.0-29.9 kg/m CONCLUSIONS: Medication use during pregnancy is prevalent, with many pregnant mothers taking multiple medications. Given the rising maternal age, body mass index, and morbidities in pregnancy, the use of medications during pregnancy is increasing. Such use correlates with an increased chance of adverse pregnancy outcomes. In the context of limited trials on the safety and efficacy of medications in pregnancy, timely harnessing of the information available within routine medical records for post-marketing surveillance is important.