From: Rabbi Moshe Sofer
To: Rabbi Naftali
The Chasam Sofer rules that no valid chazakah exists establishing that this woman's nursing causes infant deaths, because the Talmud never recognizes such a chazakah, the pattern of deaths is non-consecutive and alternating, and the twin case demonstrates the milk is nutritionally insufficient rather than toxic. Practically, he rules that the woman should nurse initially, and after some days a qualified doctor should examine the milk; if the doctor declares it poisonous, his testimony suffices to prohibit nursing even without compelling the father to hire a wet-nurse.
Source: Shu"t Chasam Sofer EH I §136