“Sarah laughed to herself, saying, “After I have become old, shall I have pleasure, my lord being old also?” Gen. 18:12

Sarah laughed just as Abraham did (17:17), though not necessarily in the same manner.  God already determined the child’s name would be Isaac (which in Hebrew, Yitzchak, means laughter).  Though Abraham and Sarah receive a name change, as does Jacob later, Isaac and Ishmael do not, as they were named from God before they were born (16:11 and 17:19).