Cancer in pregnancy has an incidence of approximately 1:1000, and cases of sarcoma in pregnancy are rare, with only a few described in the literature. This case report describes a 32-year-old pregnant woman who noticed an approximately 3.0 cm nodule on her left flank in the second trimester of pregnancy. Initially, it was diagnosed as a lipoma. The lesion grew progressively and after 5 months, at 25 weeks' gestation, the lesion became painful, bulky, with areas of necrosis and infection, and emitted a foul odor. Magnetic resonance imaging described the lesion as a heterogeneous mass measuring 12.0 × 10.0 × 9.6 cm on the left posterolateral abdominal wall, involving subcutaneous tissue and abdominal muscles. Oncologic treatment with neoadjuvant chemotherapy was initiated, and 1 month later, at 29 weeks, obstetric ultrasound revealed fetal growth restriction (FGR). During one of the fetal vitality assessments, oligohydramnios and umbilical artery Doppler with reverse diastolic flow were observed, leading to an emergency cesarean section at 31 weeks. The newborn died 4 days after delivery. Chemotherapy continued, and after the third cycle, the lesion was completely excised. Anatomopathologic examination and immunohistochemistry were consistent with embryonal rhabdomyosarcoma. The patient was referred for adjuvant radiotherapy to supplement treatment. This case report discusses aspects related to the frequency of sarcoma in pregnancy, diagnostic difficulties, the frequency of fetal vitality assessments, and possible therapeutic approaches during pregnancy.