From: Rabbi Moshe Sofer
To: Rabbi Amram
The Chasam Sofer addresses whether the Magen Avraham's principle of tehora belu'a makes the Rokeach's sfek sfeka unnecessary for permitting a pregnant Kohen's wife to enter an ohel ha-mes. He argues via a memah nafshach: if the fetus is part of the mother, no prohibition exists for the woman at all (bnei Aharon excludes women); if the fetus has independent status, tehora belu'a applies — either way, the Magen Avraham's point is vindicated. He also reinterprets the Rokeach's nefel language as referring to the fetus's current incomplete state rather than the possibility of future miscarriage.
Source: Shu"t Chasam Sofer YD §354