Responsa for Yevamot 73:9
אי כל היולדת לתשעה עוברה ניכר לשליש ימיה הא מדלא הוכר לשליש ימיה עוברה ודאי בר שבעה לבתראה הוא אלא אימא רוב היולדת לתשעה עוברה ניכר לשליש ימיה והאי מדלא הוכר לשליש ימיה איתרע ליה רובא
[her presumption to belong to] the majority is impaired'. If in the case of every woman, however, who bears at nine the embryo is recognizable after a third of the period of her pregnancy. it is obvious that with this [woman], since her embryo had not been recognized after a third of the period of her pregnancy, it must be a seven-months child of the second<span class="x" onmousemove="('comment',' Lit., 'last'. ');"><sup>24</sup></span> husband! — But say rather: When a woman bears at nine months, her embryo in most cases is recognizable after a third of her pregnancy. and with this woman, since her embryo was not recognized after a third of the period of her pregnancy, [her presumption to belong to] the majority is impaired.
Teshuvot Maharam
A. A person who married a nursing widow must divorce her, even though he was of priestly lineage and consequently could not remarry her, once he divorced her. The wet-nurse's vow is of no avail since her husband could annul it even though it was made Al Daat Rabbim.
SOURCES: Pr. 864; Tesh. Maim. to Nashim, 24; cf. R. Asher, Responsa, 53, 2; Tur Eben Haezer 13.