Sforno on Genesis 25:22/ספורנו על בראשית כ״ה:כ״ב

1ותאמר אם כן, after it is a fact that these fetuses already are at each other’s throats I have reason to be afraid that one of them will die so that I endanger myself by giving birth to them, causing one of them to be stillborn.

2למה זה אנכי, why were my relatives so concerned that it would be I who provide the seed for Yitzchok when they said את היי לאלפי רבבה, “may it be you who will be the source of millions.” (24,60) Also, why did my husband insist that I become the mother of his children?