i.e. God greatly increased their families both in children and posterity, and in wealth, and other outward blessings. So this phrase is used Genesis 30:30 Deuteronomy 25:9 1 Samuel 2:35 1 Kings 2:24, 1 Kings 11:38 Psalms 127:1. As houses are commonly put for families, so building is put for procreating of children, Genesis 16:2, Genesis 30:3.
Related Commentaries of Exodus 1:21
Exodus 1:21
21 And it came to pass, because the midwives feared God, that he made them houses.