From: Rabbi Akiva Eiger
To: Rabbi Eliyahu
Rabbi Akiva Eiger rejects a proposed leniency permitting cohabitation after a yoledes immersed and then saw blood during her yemei tohar. The Teshuvos Maimoniyos merely weakens proof from the Rif but does not affirmatively permit dam tohar after immersion, and the established custom endorsed by the Rambam, Ramban, and Rashba forbids cohabitation on dam tohar under all circumstances. The woman must therefore count seven clean days and immerse anew.
Source: Shu"t Rabbi Akiva Eiger §59