Is the Hajj valid if it was preceded by a miscarriage of a fetus 43-45 days old, with light bleeding, and applying the rulings of istihadah (irregular vaginal bleeding outside of menstruation or postpartum bleeding)?

The blood discharged due to a miscarriage is considered irregular bleeding (dam fasad) that does not prevent prayer if no formation (takhalluq) is apparent in the miscarried fetus, or if it does not coincide with the woman's customary period. The minimum period for formation to become apparent is eighty days. Therefore, your Hajj is valid, and nothing is required of you.