Thank you for your Question.
One is said to have a pattern in haidh if a single thing has happened for two months in a row.
So e.g. if one has always had her period for 7 days but for the past 2 months it has been 9, then her new pattern is 9.
Also, any blood seen under ten days, even if just brown and dark spots is till counted as haidh.
Hope this was useful