In attempting to understand the cncept of Yibum, we have the following questiions:
1. Is there a waiting period before yibum to establish that the yavamah
is not pregnant from the deceased husband?
2. Can a pregnant woman become a zekukah?
3. We assume that if a yevamah gives birth to her deceased husband's
child, she is free of yibum and does not require chalitzah. Should the
child die, we assume the yavanah then qualifies for yibum or chalitzah.
Is this correct?
4. A yavamah who has a living child when her husband dies, and later the
child dies, does she fall to the brother?
Dov Ber Eliezer Krieger
1. Yes, as the Mishnah states later (41a). One must wait three months before doing Yibum or Chalitzah.
2. The Mishnah later (35b) states that if a woman was pregnant and the baby that was born thereafter survived, she has no obligation for Yibum. But if the child does not survive (see next answer), she falls to Yibum.
3. Only if the child dies within thirty days -- thus clearly showing that the child was not one that could survive -- does she then fall to Yibum (ibid., and Yevamos 87b). Otherwise, if the child lived longer than thirty days and then died, she does not do Yibum, because of the principle of "Deracheha Darchei Noam" (see Insights to Yevamos 30:1:b).
4. No (Yevamos 87b; Tosfos 2a, DH v'Achos; see previous answer).