Matthew Poole and continuators on Genesis 20:18

18 For the LORD had fast closed up all the wombs of the house of Abimelech, because of Sarah Abrahams wife.

This phrase elsewhere notes barrenness, as 1 Sam. 1. 5, 6. and so many understand it here. Against which some learned men object, that that could not so soon be discovered, for all this happened between the Conception and birth of Isaac. Which objection may seem not valid, because the evidences of of Womens being with Child go so long before the birth of the Child, and those evidences not appearing in any of their Women, who before that time were generally fruitful and child-bearing, they might discern Gods hand in it, especially upon Gods admonition to their King. But because this history seems to have been done in a far less space of time, it not being probable either that God would suffer Sarah to be long with Abimelech ere he warned him, or that he being warned and so severely threatned and actually punished would delay the execution of Gods command, or that upon his obedience to God, the mercy and deliverance promised would be delayed by God. That seems more probable which others think, that this was an indisposition or plague or sore in the secret parts, by which they were hindred from cohabitation, and mutual converse, and consequently, from hopes of conception and Child-bearing, upon the removal whereof it is said that they bare Children, where, as oft-times in Scripture, the last and consummating act is put for all the proceeding acts, q. d. And they were restored to the Conjugal use, and Conception, and, in due time, to Child-bearing.