Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 6 6 2022 04 12 259 264 Ameneh Abiri Department of Obstetrics and Gynecology, Arash Hospital, School of Medicine,Tehran University of Medical Sciences, Tehran, Iran. Masoumeh Saleh Department of Obstetrics and Gynecology, Arash Hospital, School of Medicine,Tehran University of Medical Sciences, Tehran, Iran. Azadeh Shabani Preventative Gynecology Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 2021 03 16 2021 04 10 Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a disease that affects babies in which the platelet count is decreased because the mother's immune system attacks her fetus platelets. A low platelet count increases the risk of bleeding in the fetus and newborn. FNAIT is the leading cause of severe thrombocytopenia in the fetus and neonate. The most serious complication of FNAIT is intracranial hemorrhage, which occurs in 10-20% of symptomatic infants. If the bleeding occurs in the brain, there may be long-term effects. The Pathophysiology of atraumatic fetal subdural hematoma (SDH) remains unknown and is extrapolated from SDH of shaken baby syndrome in infants (1, 2). Detailed prenatal investigation is crucial to elucidate the underlying etiology, which may be associated with a better prognosis. We present a case of antenatally diagnosed SDH secondary to FNAIT that was normal up to one month after follow-up. https://crcp.tums.ac.ir/index.php/crcp/article/view/499