A number of Mishnayot here in the sixth perek of Massekhet Yevamot focus on the commandment of peru u’revu – the mitzva of having children. The Mishna on our daf teaches that this commandment is so important that if a couple has been married for ten years with no children, the husband cannot choose to simply forgo this mitzva (in the time of the Mishna he could choose to marry a second wife). The baraita teaches that should he choose to divorce her, he is obligated to pay her ketuba, and she can marry another. Both of these rulings indicate that we do not assume that the onus of responsibility for the lack of children rests with the wife, rather the couple may simply not have been compatible.
From a medical perspective, it is possible that both husband and wife could be physically able to conceive, yet they cannot have children together, that is to say that a variety of issues may keep the woman from becoming pregnant or not allow an embryo to develop after conception. Sometimes the woman’s body may have antibodies that do not allow for a specific man’s semen to survive, which will keep any pregnancy from developing; in other cases the genetic combination of the couple may create conditions that kill the embryo before it advances in its development.
These considerations bring the Ritva to rule that even if the husband has had children from a previous marriage, that in itself does not prove that the husband is healthy and that it is his wife who cannot conceive, for it is possible that she, too, can have children, just not with him. For this reason, in the event of a divorce, such a woman can marry another man, and even if she has no children in the second marriage, she can marry a third time, as well.