Aitareya Upaniṣad 2.1.3

2.1.3

sā bhāvayitrī bhāvayitavyā bhavati.
taṃ strī garbhaṃ bibharti.
so 'gra eva kumāraṃ janmano 'gre 'dhi bhāvayati.
sa yat kumāraṃ janmano 'gre 'dhi bhāvayaty ātmānam eva tad bhāvayaty eṣāṃ lokānāṃ santatyai.
evaṃ santatā hīme lokāḥ.
tad asya dvitīyaṃ janma.

3. She, being a nourisher, should be nourished. The woman bears him as an embryo. In the beginning, indeed, he nourishes the child [and] from birth onward. While he nourishes the child from birth onward, he thus nourishes his own self, for the continuation of these worlds; for thus are these worlds continued. This is one's second birth.