Dear Rabbi Kornfeld,
I once asked you a question to define when and what shilya is. I suspect that you had no time to go into this. So, let me try. It is clear that it is the embryonic sac. We know now that all the parts are there in the egg in potentia. The shilya becomes more and more differentiated as time progresses. (As well as after birth which is a more advanced state.) We have a phrase in the sugya on pg. 29a "hipilah ruach".
So, it is not a ledah even though a sac was aborted if it is empty The gemoroh quantifies this as "before huchzaka ubrah". The Nodah Biyehuda equates that to "hukar.." which is 3 months. So, it cannot be called shilya till then. Even though the Chasam Sofer makes it much earlier-still I would suspect he agrees about shilya. The two are not arguing when it is called shilya. So, I suppose it cannot be before three months.
Therefore, if a doctor would say that the sac is empty-no fluids that are tell tale signs of aborted fetus we would (before 3 months) if we accept the rofiim define it as hipilah ruach. Also, even if a doctor said he saw a fetus even at 75 days whose groth was arrested before 40 days we might call it a shapir sheno merukam. But, these are horooh issues if we have no halachic shilya.
Here are some comments:
1. Medically, there is a "blighted ovum" which develops for several weeks and aborts: a sac and placenta with no identifiable embryo inside. This is likely to be the "ruach". I can't find a source for saying that a "ruach" is empty of fluids. There is also a "molar pregnancy", in which a growth akin to cancer develops inside a placenta and sac, sometimes for many months. This is probably a kind of "nefel" or "guf atum".
2. Rashi in Brachos 4a (uvshilia) has a nice definition and description of a shilia. He quotes the gemara in Nidda 26a that says that a shilia has a minimum size of 1 tefach and starts as an "eirev" string. That seems to include the placenta as well as the sac.
3. I can't find "hipila ruach" on Nidda 29a.
4. See Tosphos on Shavuos 8a (v'aima yoledes).
5. I think Rabbi Beilin (please send him my regards) is trying to reconcile "ain shilia b'lo valad" with the idea of "hipila ruach" and that we assume most miscarriages after "hukar ubra" are not "ruach". This seems to indicate that the shilia does not normally reach minimum size until around 3 months. The fetus is about 1 centimeter long at 6 weeks and about 5 centimeters at about 3 months.
6. I am forwarding your email to Dr. Pollack.