When her days to give birth were completed, behold, there were twins in her womb.
24. And when her days to be delivered were fulfilled. Moses shows that the intestine strife in her womb continued to the time of bringing forth; for it was not by mere accident that Jacob seized his brother by the heel and attempted to get out before him.
We have here an account of the birth of Jacob and Esau, the twin sons of Isaac and Rebekah: their entrance into the world was (which is not usual) one of the most considerable parts of their story; nor is much related concerning Isaac but what had reference to his father while he lived and to his sons afterwards.
Commenting on Genesis 25:19-28
And when her days to be delivered were fulfilled,.... The nine months were up from the time of her conception; or, as the Targum of Jonathan, when the two hundred and seventy days she went with child were completed: behold, there were twins in her womb; as was perceived by the midwife; a double mercy was granted, more given than asked for; probably only one...