One of the basic sources in the Talmud that deals with issues of birth control appears on our daf.
Rav Beivai taught a baraita before Rav Nahman. Three categories of women may use a mokh (an absorbent cloth) while engaged in marital relations – a minor, a pregnant woman and a nursing woman. The minor, because she might become pregnant and as a result might die.
In Massekhet Yevamot (12b) Rav Beivai’s explanation continues:
A pregnant woman may use a mokh because she might cause her fetus to degenerate into a sandal (a formless creature); and a nursing woman, because she might have to wean her child prematurely, which may result in its death. What is the age of such a minor? From the age of eleven years and one day until the age of twelve years and one day. One who is under or over this age must carry on her marital intercourse in the usual manner. This is the opinion of Rabbi Meir. The hakhamim say that all women should carry on marital intercourse in the usual manner, and heaven will have mercy on them (i.e. no harm will come to them), based on the passage that states (Tehillim116:6) “HaShem preserves the simple.”
The rishonim differ as to how to understand this baraita and what its implications are for the halakha. According to Rashi, the discussion is whether a woman can insert a physical barrier into her vaginal canal as a means of birth control. Rabbi Meir’s position is that a woman who has reason to fear that pregnancy will result in a danger to her or to her unborn child is permitted to do so, although it would be forbidden to other women. Tosafot and others reject Rashi’s explanation, arguing that inserting a mokh during relations would be forbidden. They suggest that the mokh is an absorbent cloth that is inserted following sexual relations in an attempt to remove the semen. According to Rabbi Meir, a minor as well as a pregnant or nursing woman would be obligated to use this mokh in an attempt to keep a potentially dangerous pregnancy from developing (a method that is recognized today as being of limited use, if any), while other women would be permitted to do so.