Does the blood discharged by a pregnant woman, in her first month and a half, which the doctor says will lead to a miscarriage, invalidate prayer as menstrual blood?

This blood is in all cases the blood of istihada (irregular bleeding); a pregnant woman does not menstruate, and whatever she sees is istihada. Even if the bleeding occurs after a miscarriage where the fetus's creation was not yet discernible, it is still istihada blood. A woman experiencing istihada must take precautions and perform ablution (wudu') for each prayer after its time has entered, and she should pray both obligatory and supererogatory prayers. Her ablution is not nullified except by the expiry of the prayer time or by one of the known nullifiers of ablution.