Introduction: Fetal intrapericardial teratoma is a rare tumor that can be diagnosed by antenatal ultrasonography early in pregnancy. Case Presentation: A fetal intrapericardial teratoma was detected on routine ultrasonography in the second trimester of pregnancy. At 31 weeks gestation, a marked increase in tumor size, fetal ascites, and pericardial effusion were observed, indicating that preterm delivery would be inevitable. Corticosteroid prophylaxis (24 mg of betamethasone in two doses of 12 mg 24 h apart) initiated for prophylaxis of respiratory distress syndrome led to a reduction in fetal ascites and pericardial effusion. Betamethasone therapy (4 mg/per day) was continued with the aim to postpone the expected date of delivery. Gestation was extended for more than 2 weeks. At 33 weeks and 5 days gestation, the neonate was delivered by elective cesarean section with ex utero intrapartum treatment and immediately submitted to fetal cardiac surgery. The infant was discharged from the hospital in good health about 4 months later. Conclusion: The present report draws attention to improvement in fetal status and extension of gestation achieved with maternal low-dose corticosteroid therapy on antenatal ultrasound finding of fetal ascites and pericardial effusion due to intrapericardial teratoma.