With this in mind, the linked question you begin with on whether Githzerai lay eggs remains the answer to this one: They do (MM, 87). Githyanki hatch from eggs.

How do Githyanki reproduce?

Githyanki reproduced by laying eggs. It was unknown whether this trait had been acquired during their period of enslavement or as a result of exposure to the Astral Plane.

Where are the GITH from?

Gith was once a slave of the vast illithid empire, although she later led her followers to the Astral Plane after defeating their illithid masters.