Abram took his wife Sarai and his nephew Lot, and all their possessions which they had accumulated, and the people which they had acquired in Haran, and they set out for the land of Canaan; so they came to the land of Canaan.
Genesis 12:5 (NASB)
If you recall that “people which they acquired” is literally “the living souls they made,” you’ll see Abram and Sarai were given the power to be fruitful and multiply, even though Sarai is barren. Being fruitful and multiplying is a spiritual blessing, and God makes it happen, long before Sarai miraculously gives birth to Isaac.
Nothing is impossible for God.