וַיִּמְלְא֥וּ יָמֶ֖יהָ לָלֶ֑דֶת וְהִנֵּ֥ה תוֹמִ֖ם בְּבִטְנָֽהּ׃
And when her days to be delivered were fulfilled, behold, there were twins in her womb.
Read Kabbalistic (mystical) interpretations of Genesis 25:24: Zohar and classical Jewish mystical sources, free online.