So Abraham prayed to God; and God healed Abimelech, his wife, and his female servants. Then they bore children; for the Lord had closed up all the wombs of the house of Abimelech because of Sarah, Abraham’s wife.
Genesis 20:17-18 (NKJV)
Abraham’s prayer at the end of Genesis 20 should surprise the reader, because his own wife is barren. It is meant to be ironic.
The rabbis have a saying about prayer: if you earnestly pray for someone who has a need, but you also have that need, God answers your need first.
And the Lord visited Sarah as He had said, and the Lord did for Sarah as He had spoken.
Genesis 21:1 (NKJV)
The “And” in Genesis 21:1 is meant to link this text to the end of Genesis 20 to show God answering this prayer for Sarah.