From: Rabbi Moshe Sofer
To: Rabbi Moshe
A widow who concealed a premarital pregnancy does not lose her tosefes kesubah, as the Maharit's relevant ruling was tentative and not definitive, and the Be'er Heitev's citation of it was misleading. She is not considered overes al das because that concept applies only to ongoing future risk of causing the husband to stumble, not to a past transgression. Nevertheless, the husband may divorce her against her will without violating the Cherem d'Rabbeinu Gershom, since her concealment constitutes legitimate grounds for dissatisfaction.
Source: Shu"t Chasam Sofer EH I §148