Shatapatha Brahmana 7.1.1.20

7.1.1.20

taṃ vai pakṣapucavantameva santam | na pakṣapucavantamiva paśyanti tasmādyonau garbhaṃ na yathārūpam paśyantyathainamamutra pakṣapucavantam paśyanti tasmājjātaṃ garbhaṃ yathārūpam paśyanti

While being indeed furnished with wings and tail, people do not see him as one having wings and tail: hence one does not see the child in the womb in its proper shape; but hereafter they (will) see him as one having wings and tail, and hence one sees the child after it is born in its proper shape.