Clotting factor VII during pregnancy, delivery and puerperium

Summary. During pregnancy the activity of coagulation factor VII in plasma increases up to 248% (SEM 16) (n=18) at 40 weeks even when all precautions to avoid cold activation are taken. This increase is at all times during pregnancy, delivery and puerperium entirely due to the presence in vivo of what is most likely a phospholipid-factor VII complex. This complex is sensitive to phospholipase C, so that treatment with the enzyme reduces the activity of pregnant plasma down to that of non-pregnant controls. When present in the complex factor VII has a higher specific activity and an altered conformation with a more accessible active site as demonstrated by increased susceptibility to inactivation by diisopropylfluorophosphate. Factors II and X are increased to 136% (SEM 4) and 171% (SEM 6) (n=18) without being sensitive to phospholipase C. The increase during pregnancy and the decrease after delivery of the phospholipase-sensitive factor VII activity have been followed.