The Mishna on our daf continues the discussion of the mitzva of peru urvu – literally “to be fruitful and multiply (i.e. the commandment to have children). Here we learn that the opinion of the Tanna Kamma is that only males are obligated in this commandment, although Rabbi Yohanan ben Beroka disagrees, pointing to the passage in Sefer (1:28) where God blesses both Adam and Eve and commands them to be fruitful and multiply.
In explanation of the Tanna Kamma’s position that women are not obligated in this mitzva, the Gemara brings Rabbi Ile’a quoting Rabbi Elazar b’Rabbi Shimon who argues that the conclusion of the passage referred to above adds ve’khivshuha – “and conquer it.” Thus, the commandment to have offspring includes a mitzva to conquer and control the world, something that is perceived as being a male oriented endeavor.
To support the ruling that the mitzva applied only to men, the Gemara relates a story about Rabbi Hiyya’s wife, Yehudit, who had given birth to two sets of twins – two boys and two girls – and had found the birthing experience to be particularly difficult and painful (the Gemara relates that one set of twins – Yehuda and Hizkiyya – were born almost two months apart). She went in disguise to her husband, Rabbi Hiyya, and asked whether women are obligated in the mitzva of peru urvu. When he ruled that they are not commanded, she drank a potion that made her sterile, so that she would have no more pregnancies. When Rabbi Hiyya learned what had happened, he lamented that he would have wanted one more set of children.
In fact, research has found that some women are more likely to give birth to twins than others (this trait often runs in families). Thus, a woman who has already had two sets of twins will likely conceive twins again – a fact that was of particular concern to Rabbi Hiyya’s wife who had found those pregnancies so difficult.