From: Rabbi Moshe Sofer
To: Rabbi Aryeh Yehuda Leib Toiber
An unmarried woman pregnant by a Kohen sought to marry him, raising concern that she may have had prior relations with a non-Jew (rendering her a zonah). After personally interviewing the woman in Pressburg and confirming she lived in a predominantly Jewish alley with no need to frequent non-Jewish areas, and that she had been exclusively designated to this Kohen, the Chasam Sofer ruled she is permitted to marry him. This conclusion rests on the Rema's ruling that mutual admission is believed for Kehunah purposes, the Rashba's position that a Jewish neighborhood constitutes its own majority, and his own view that the Sages' concern about disqualifying relations does not extend to uncircumcised non-Jews.
Source: Shu"t Chasam Sofer EH II §121