Know that sometimes a man may reincarnate into the body of a woman, because of a sin, (cultural context) or something similar. Now this woman who has received the soul of a man, will not be able to conceive and become pregnant.... This woman will need great merit to enable her to become pregnant and give birth. The only way it can be done is that some other feminine soul must enter her as an ibur.
However, she cannot give birth to sons for two reasons. The first is [as follows:] There is a verse that says, "…If a woman puts forth seed, and a male child is born" (Lev. 12:2). In this case, the woman is a male, just like her husband. She cannot give birth to boys, only to girls.
The second reason is that the feminine soul that has entered her does so only as an ibur, in order to help her become pregnant and give birth. Once this woman gives birth, that soul does not need to stay there any longer for no reason. And then, at the time that she gives birth, that [feminine] soul enters into the fetus as an actual Gilgul, and not as an Ibur, like it was at first. That is why the child that is born most be female and not male. (the text goes on the explain how sometimes it is possible for her to give birth to a male soul, when the male soul currently in her enters to child, and several other scenarios).