Another interpretation: "As he shall lay upon him" (Exodus 21:22). I might understand this to apply even though the pregnancy is not his; therefore Scripture says "with child," [restricting it to his own]. Another interpretation: "As he shall lay upon him" -- I might understand he may impose whatever he wishes; therefore Scripture says "and he shall pay as the judges determine" (Exodus 21:22), telling us that he pays only according to the judges. As it is said, "and he shall pay as the judges (pelilim) determine" -- these are the judges, as it is said, "and our enemies being judges (pelilim)" (Deuteronomy 32:31); and it says, "If a man sin against a man, the judges (Elohim) shall judge him" (1 Samuel 2:25).
Damages for the Unborn Are Fixed Only by the Judges
Yalkut Shimoni on Torah 335:10
דָּבָר אַחֵר, כַּאֲשֶׁר יָשִׁית עָלָיו, שׁוֹמֵעַ אֲנִי, אַף עַל פִּי שֶׁאֵין הַהֵרָיוֹן שֶׁלּוֹ, תַּלְמוּד לוֹמַר הָרָה. דָּבָר אַחֵר, כַּאֲשֶׁר יָשִׁית עָלָיו, שׁוֹמֵעַ אֲנִי כָּל שֶׁיִּרְצֶה, תַּלְמוּד לוֹמַר וְנָתַן בִּפְלִלִים, מַגִּיד שֶׁאֵינוֹ מְשַׁלֵּם אֶלָּא עַל פִּי הַדַּיָּנִים, שֶׁנֶּאֱמַר וְנָתַן בִּפְלִלִים, אֵלוּ דַּיָּנִים, שֶׁנֶּאֱמַר וְאֹיְבֵינוּ פְּלִילִים, וְאוֹמֵר (שמואל א ב, כה) "אִם יֶחְטָא אִישׁ לְאִישׁ וּפִלְּלוֹ אֱלֹהִים".