BACKGROUND Primary splenic cysts are very rarely diagnosed in pregnancy, with only thirteen cases described in the literature. We examine the approach towards diagnosing and managing uniquely large abdominal masses that significantly complicate obstetric care. METHODS A 37-year-old primigravida woman presented with abdominal distension and discomfort, yet otherwise asymptomatic. On ultrasound, an incidental pregnancy at 25 weeks of gestation and a large pelvic lesion were discovered. MRI defined a 28 × 29 cm lobulated, complex cystic mass in the upper abdomen. The patient underwent two ascitic drainages throughout her pregnancy. At 34 weeks of gestation, she had a classical caesarean section. Then at five-weeks postpartum, she underwent a laparotomy and total splenectomy with 16 L of fluid drained. Histopathological analysis revealed an epithelial cyst of the spleen. Her recovery was complicated by complete portal vein thrombosis. CONCLUSIONS This case describes the largest splenic cyst ever reported in pregnancy and explores the diagnostic dilemmas and treatment challenges associated. We introduce the utility of serial ascitic drainages in prolonging the pregnancy and emphasise the reliance on imaging for surveillance of splenic size and fetal wellbeing.