Hello. Everyone holds that shechita on the mother behama helps to be matir the vlad. According to the m'an d'amar that Uber L'av Yerech Ima wouldn't a person be oiver the L'av of Oisah v'es B'nah by shechting the mother cow.
Thank You
The Or Same'ach (Shechitah 12:10) says that the fetus does not really need Shechitah, since we learn from the Pasuk of "ba'Beheimah" that it may be eaten if it's mother was slaughtered correctly. Therefore, even if it was slaughtered, it does not have the prohibition of Oso v'Es Bno, since it would have been permitted without this Heter.
Tevu'os Shor (16:2) and the Pri Megadim (Sifsei Da'as 16:3 DH Kasav) discuss whether a mother and child which were slaughtered simultaneously, have the prohibition of Oso v'Es Bno.
Perhaps we could also answer that since the child is not killed by this Shechitah it is not included in the prohibition. (This may fit in with the Rambam that the prohibition of Oso v'Es Bno is to prevent the slaughtering of a child in front of its mother's eyes. This is obviously not applicable here.)
A further possibility may be that the fetus in the mother's womb is not included in the word Bno and hence not covered by this prohibition.
Dov Freedman