Gestational diabetes is associated with increased risk for venous thromboembolism. Activation of sympathetic nervous system affects blood coagulation, fibrinolysis and platelet activation by several mechanisms. We aimed to study the relationship of sympathetic nervous system, coagulation and platelet function in gestational diabetes. Forty-one white women with gestational diabetes, 22 healthy pregnant and 14 nonpregnant controls were studied. We assayed serial nocturnal (at 12 p.m., 4 a.m. and 7 a.m.) changes of the adrenergic transmitter noradrenaline, coagulation variables and platelet activation with PFA-100. Plasma noradrenaline increased from 4 to 7 a.m. in both pregnant groups. During the same time period, prothrombin time (PT) shortened in gestational diabetes compared with healthy pregnant and nonpregnant controls. In gestational diabetes, nocturnal FVIII:C levels were lower compared with normal pregnancy and also variables associated with von Willebrand factor tended to be lower. Platelet activity increased at midnight in pregnant women compared with nonpregnant women without differences between gestational diabetes and normal pregnancy. Gestational diabetes is associated with concomitant early morning sympathetic stimulation and activation of extrinsic coagulation pathway (shortened PT). Decreased FVIII:C may refer to compensatory anticoagulatory mechanism. These alterations could reflect increased risk of pregnancy-related thromboembolism in gestational diabetes.