Śatapatha Brāhmaṇa ("of a hundred paths") 2.2.1.10

2.2.1.10

sa yadagnaye pavamānāya nirvapati | prāṇā vai pavamāno yadā vai jāyate 'tha prāṇo 'tha yāvanna jāyate māturvaiva tāvatprāṇamanu prāṇiti yathā vā tajjāta evāsminnetatprāṇaṃ dadhāti

Now the reason why he makes offering to Agni Pavamâna, is that the blowing one is the breath. When (the child) is born, then there is breath. And as long as it is not born, it breathes in accord with the mother's breath; but when it is born, then he thereby puts breath into it.