John Gill Commentary Genesis 20:18

"For Jehovah had fast closed up all the wombs of the house of Abimelech, because of Sarah, Abraham`s wife." — Genesis 20:18 (ASV)

For the Lord had fast closed up all the wombs of the house of Abimelech With large tumours probably, so that they could not cohabit with their husbands and conceive; nor could those that had conceived bring forth: and this disorder they were smitten with, because of Sarah Abraham's wife ; who was taken into the house of Abimelech, in order to be his; to rebuke and punish for which, and to convince of the evil of it, and cause to abstain from it, this disorder was inflicted on them.