Targum Isaiah 66:7–8 — as quoted by Pitre (p 121); translation: Bruce Chilton, The Isaiah Targum (Aramaic Bible 11)
Before distress comes to her she shall be delivered; and before shaking will come upon her, as pains upon a woman in travail, her king will be revealed. Who has heard of such a thing? Who has seen such things?
No freely usable English translation of this passage is online, so the note keeps Pitre's quotation and links to the full text. Translation: Bruce Chilton, The Isaiah Targum (Aramaic Bible 11), as quoted by Pitre.
Why Pitre cites it
'Before distress comes to her she shall be delivered… her king will be revealed.' The Targum links Isaiah's painless birth with the coming of the king.