Background <p>Multimorbidity during pregnancy, the coexisting of two or more chronic health conditions, is linked to negative impacts on foetal development, adverse birth outcomes, and increased risk of future health problems for mother and child. While existing research has explored single chronic conditions in relation to pregnancy outcomes, there remains a significant gap in understanding how multimorbidity influence maternal and neonatal health. This review aims to identify, assess, and synthesise literature on multimorbidity during pregnancy and its adverse perinatal and neonatal clinical outcomes to inform future research and public health interventions.</p> Methods <p>We conducted a systematic review of perinatal and neonatal outcomes, following the PRISMA 2020 guidelines. Embase, Web of Science, and Medline databases were searched to find relevant cohort and case-control studies published (January 1, 2015-March 3, 2025). There were no restrictions on setting or language. A narrative synthesis was conducted to summarise the existing findings between multimorbidity during pregnancy and adverse outcomes in offspring.</p> Results <p>Of 7,531 publications screened, 54 articles were included. Most studies (<i>n</i> = 28) reported on pregnant women with multiple physical non-communicable diseases (NCDs), followed by those with infectious diseases (<i>n</i> = 11), two or more mental health conditions (<i>n</i> = 5), environmental exposures (<i>n</i> = 3), comorbid physical NCDs and mental health conditions (<i>n</i> = 5), and substance use (<i>n</i> = 2). The most common outcomes reported were preterm birth (<i>n</i> = 30), neonatal intensive care unit admission (<i>n</i> = 15), low Apgar scores (<i>n</i> = 13), neonatal mortality (<i>n</i> = 13), and small-for-gestational age (<i>n</i> = 13). This systematic review also revealed that there is variance in how multimorbidity is defined and how neonatal outcomes are measured and recorded, including the terminology used, values for adverse outcomes, and the points at which the outcomes were measured.</p> Conclusions <p>This review identified adverse outcomes associated with multimorbidity during pregnancy and highlighted the need to shift research priorities towards multimorbidity research, especially in lower-income countries. A concrete definition of multimorbidity and a globally standard set of measurements to be recorded at birth are needed to facilitate research that is generalisable across contexts. By identifying pregnancy outcomes in women with multimorbidity, vulnerable populations can be targeted for more effective interventions.</p>