Q) Can I attribute blood found on a bedika cloth to a wound during the first three days of shivoh nekiyim?
A) The Remo (YD 196:10) quotes an opinion that maintains that during the first three days of shivoh nekiyim one cannot attribute a kesem to an extrauterine source [in order to render the lady tehora]. This means that although we find earlier in Hilchos Niddoh (Siman 190) that a kesem can be attributed to an extrauterine source [and the lady will remain tehora/the shivoh nekiyim will not be affected]; within the first three days of shivoh nekiyim a teliya (attribution to an extrauterine source) cannot be made, and the lady is therefore temei’oh.
• The Remo limits this stringency to a kesem that is larger than the size of a gris; if a kesem is smaller than the size of a gris it is automatically tehora.
• The Remo also mentions that this stringency is only said regarding a regular teliya; however, if a lady is being toleh the kesem found to a wound on her body that she knows is emitting blood – it is possible to attribute the blood to the wound even in the first three days of shivoh nekiyim.
Rav Akiva Eiger writes that this leniency of the Remo [attributing blood to a wound that is known to be emitting blood within the first three days of shivoh nekiyim] applies specifically to a kesem; however, blood found on a bedika cloth is more severe (i.e. it potentially renders her a niddah min hatorah) and therefore being toleh blood found on a bedika cloth to an extrauterine source during the first three days of shivoh nekiyim is not possible.
Rav Moshe Mordche Karp (Mishmeres Hataharoh vol. 1, perek 5) argues on the distinction of Rav Akiva Eiger and maintains that even during the first three days of shivoh nekiyim it is possible to attribute blood found on a bedika to a wound that is known to be emitting blood (since both kesomim and bedikos are d’rabonon where there is known to be a wound) as long as no hargasha is experienced.
Since the halachos governing bedikos and teliyos are intricate and complex, a question of this nature must only be answered by a competent moreh hora’ah.