I was thinking about Air again, partly because I'd been rooting around frantically for my copy of the book since Geoff Ryman was going to be at WisCon. I found the book, and then realized The Unconquered Country is a lot smaller, and I should bring that one to be signed, instead.
Back to the book's contents. To me, it's obvious that the physical floods in the book, as well as the coming of Air, sweep away an old way of life. One of the books themes is that one world is always swept away for a new one which you cannot necessarily expect, and which will always be different than you think. Mrs. Tung's flood happened before the book began, and we see it in memory fairly early on in the story. The flood in Kizuldah happens near the end, bookending, but at the same time coming before the final flood, which is the coming of Air.
But the baby. The baby is the new human, formatted by Air, living in Air, tiny and blind and, I assume, unable to live without Air. In a way, he symbolizes the new knowledge, or is the new knowledge, the new world. And his father says, chuckling, "He burns," even while he holds him close.
My new thoughts were on Mae's pregnancy. She carries the baby in her stomach. The baby's conception, supposedly, happens in the scene where she and Ken Kuei are bathing, washing each other, and having oral sex, during which Mae discovers she is menstruating; Kuei floods semen in her mouth, and Mae floods blood. I didn't immediately make the connection between the fluids there and the coming flood of both water and information. The baby comes, in a way, from flooding and is the product thereof.
One more thing. During the pregnancy, Mae suffers was sounds like severe acid reflux. It's a heavy-handed analogy, but change can be bitter, and can burn, but must be accepted. The baby is born when Air comes. Everyone is happy, and no one mentions the weird deformity of the child or seems to think it is weird, and suddenly they are getting messages through Air. Change has happened. They are accepting the future without expectation of what it will be like, except that it will be different; they are ready to go forward.