As we have learned, if a kohen marries a woman who is not from a family of kohanim, once she becomes a member of his household she will be permitted to eat teruma in his home. Conversely, if a woman from a family of kohanim marries an ordinary Jew, once she joins his household, she no longer is permitted to eat teruma.
What happens if the marriage ends?
In both such cases, once the husband dies or divorces his wife, she returns to her father’s house, and once again follows the rules that apply in that household. The exception will be if she has had children with her husband. In such a case, the child will keep her in her husband’s family’s home, and a woman married to a kohen would continue to eat teruma, while the daughter of a kohen married to an ordinary Jew would not be able to do so (see Vayikra 22:13).
The Gemara on our daf quotes a baraita that offers the following ruling. If the daughter of a kohen marries an ordinary Jew, and he dies with no children, the widow can begin eating teruma immediately. That is to say, we are not concerned with the possibility that she is pregnant with a child, something that would keep her from returning to her father’s household. Rav Hisda explains that this is true for forty days because we can work with the assumption that either she is not pregnant or else the embryo is not considered to be significant for the first 40 days.
The Rabbinic ruling that an embryo is not given halakhic significance for the first 40 days coincides with the stage of development when the embryo loses its similarity to embryos of other animals to the extent that the tail disappears and the human head, hands and legs begin to form. Although at that point the embryo is still small and undeveloped, still it is clearly recognizable as a human form.