Macrophage activation syndrome (MAS) is a complex, life-threatening, hyperinflammatory condition occurring as a form of hemophagocytic lymphohistiocytosis (HLH), commonly associated with several autoimmune and autoinflammatory diseases, and certain infections such as Parvovirus B19 (P19V). The onset of systemic lupus erythematosus (SLE) presenting as MAS during pregnancy is uncommon, posing significant diagnostic and therapeutic challenges. We present a case of a 30-year-old woman at the 12th gestational week with fever, arthralgia, rash, cervical lymphadenopathy, cytopenia, and elevated liver enzyme. Bone marrow biopsy revealing hemophagocytosis, elevated ferritin and triglycerides, high interleukin-2, fever and cytopenia, confirmed the diagnosis of HLH. Further evaluation revealed the diagnosis of SLE. Treatment was initiated with intravenous immunoglobulin and corticosteroids. Given the deterioration in the patient’s clinical condition, a decision was made to terminate the pregnancy. She continued in the following months to receive SLE treatment with corticosteroids, cyclophosphamide, hydroxychloroquine, and later with mycophenolate mofetil due to the development of Class IV of lupus nephritis. P19V IgM antibodies were initially positive, later seroconverted to IgG, indicating that infection may have acted as a trigger for the onset of SLE and MAS development during pregnancy. The overlapping clinical features of P19V infection, SLE, and MAS pose significant diagnostic and therapeutic challenges. Early recognition and comprehensive diagnostic evaluation are crucial for the management of these conditions, especially during pregnancy, where both maternal outcomes are at risk.