In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
The bleeding you are experiencing following your miscarriage after 6 weeks of pregnancy is not regarded as nifas (post-natal bleeding). Rather, it can be considered as menses unless it exceeds the acceptable duration of menses.
In other words, if the blood resembles menses in color and texture, it shall be treated as menses unless it exceeds fifteen days.
If it exceeds fifteen days, then you should bathe yourself and resume your prayer afterwards except that you are required to observe the following condition: If bleeding continues, you ought to wash your private prior to each prayer and wear a pad and perform ablutions as close to the prayer as possible. You need not worry about bleeding during the course of your prayer. Your prayer is considered valid, as long as you fulfill the above requirements.
If, however, the blood does not quite resemble menses in color and texture, then you ought to follow the normal pattern of your menses.
In other words, if you were in the habit of experiencing menses 6 or 7 days every month, then you should set aside the same number of days as your period of menses, after which you are to bathe yourself and resume your prayer.
But, while doing so, follow the same method as described above in regard to washing yourself and performing ablutions.
Almighty Allah knows best.