I've been looking at the "This is Your Life" tables from Xanathar's Guide to Everything, and in particular there's an entry on the Birthplace table on page 62:
98 On the Astral Plane or the Ethereal Plane
However, the DMG says this about the Astral Plane on page 47:
Creatures on the Astral Plane don't age or suffer from hunger or thirst. For this reason, humanoids that live on the Astral Plane (such as the githyanki) establish outposts on other planes, often the Material Plane, so their children can grow to maturity.
So it would seem that it would be impossible for an embryo to grow inside, say, a githyanki mother, so doesn't that make giving birth on the Astral Plane impossible?