Because carriers have one normal X chromosome which produces a certain amount of Factor VIII or IX clotting factor, they are protected from the most severe form of hemophilia in which the level of clotting factor is less than 1%.
However, the variation in clotting factor levels in carriers is very wide. It ranges from levels similar to those of hemophiliacs in some carriers to normal levels in others. This is because the two X chromosomes, one of which carries the hemophilia gene, are not equally functional. If the hemophilia X chromosome happens to be functional in most cells, then the carrier will have a very low level of clotting factor activity.
Many carriers have a clotting level between 30% and 70% of normal and do not usually suffer from excessive bleeding. However, some carriers have less than 30% of the normal level of Factor VIII or IX. These women are considered to be mild hemophiliacs.
In any case, all carriers should pay close attention to signs of abnormal bleeding. These signs include:
heavy, prolonged menstrual bleeding (menorrhagia)
easy bruising
frequent nose bleeds.