We experienced a case of congenital afibrinogenemia and successfully performed cesarean section with administration of fibrinogen. The patient was administered fibrinogen every week to sustain a fibrinogen level above 60 mg/ dl according to our previously reported first case. Pregnancy course was uneventful, and fetal growth was normal, but unfortunately placental abruption occurred after the spontaneous onset of labor at 37 weeks gestation. The fibrinogen level before labor was 96 mg/dl, but decreased to 33 mg/dl when placental abruption was diagnosed. During and after the operation, it was increased to 147 and 199 mg/dl, respectively, through infusion of 10 g of fibrinogen, and massive bleeding was stopped. Two grams of fibrinogen were infused daily after cesarean section, and postpartum hemorrhage was normal. It is obvious that fibrinogen is an extremely important factor in maintaining pregnancy, and we conclude that fibrinogen level must be at least 60 mg/dl during pregnancy, 120 mg/dl during surgery and 150 mg/dl during labor, if possible as high as 200 mg/dl under the continuous infusion of fibrinogen to prevent placental abruption.