The fifth aliyah tells us that Avrohom was a hundred years old when Yitzchak was born, and Rashi explains that the whole world rejoiced with Sarah because many barren woman the world over were remembered with her, and many sick people were healed.
Sarah nursed many women's children to show that she had actually given birth to Yitzchak (even though she was 90 years old).
Later, Sarah notices the bad ways of Yishmael and wants him to leave so as not to influence Yitzchak. G-d says to Avrohom: "Listen to your wife" (this verse is widely quoted to show that wives are held in such high esteem in the Jewish family).
