From: Rabbi Moshe Sofer
To: Rabbi Naftali
The Chasam Sofer rules that using a moch during intercourse is absolutely forbidden even in life-threatening situations, and no authority permits it. He suggests that using a moch after intercourse may be permissible, but only with the husband's explicit consent, since the wife has no unilateral right to destroy her husband's seed.
Source: Shu"t Chasam Sofer YD §172