39 Heb “Why, this?” The demonstrative pronoun following the interrogative pronoun is enclitic, emphasizing the Lord’s amazement: “Why on earth did Sarah laugh?”
40 The Hebrew construction uses both הַאַף (ha’af) and אֻמְנָם (’umnam): “Indeed, truly, will I have a child?”

In other versions

The Lord said to Abraham, “Why did Sarah laugh and say, ‘Shall I indeed bear a child, now that I am old?’

Then the Lord said to Abraham, “Why did Sarah laugh and say, ‘Will I really have a child, now that I am old?’

But the Lord asked Abraham, “Why did Sarah laugh, saying, ‘Can I really have a baby when I’m old?’

Then the Lord said to Abraham, “Why did Sarah laugh? Why did she say, ‘Can an old woman like me have a baby?’

Then Yahweh said to Abraham, “What is this that Sarah laughed, saying, ‘Is it indeed true that I will bear a child, now that I have grown old?’

And the Lord said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old?

Public Domain