>>… why so narrow a class ? (almost a "sub-group" !?) <<
It’s not a subgroup. Surgery or childbirth are the times when individuals with hereditary antithrombin deficiency must have their level of AT brought up to the normal range. Not to do so risks a fatal blood clot during the procedure.
In everyday life, individuals with HD can manage with an oral anticoagulant such as Warfarin, but an oral anticoagulant cannot be taken during surgery/childbirth due to the risk of bleeding.
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