When you have a kid and insurance, typically you call the insurance company to add them to your policy. The premium goes up, and you're done. If insurance has been covering OB/GYN visits and the delivery, they may even be expecting it.
When you buy your insurance through healthcare.gov, though, you need to update your policy with the government's Medicare agency, which recalculates your tax credit, and which may or may not increase your cash outlay. And which may or may not make you eligible for Medicaid, even, under the expanded coverage.
Unfortunately, you can't do that on the healthcare.gov site yet. So you have to call your insurance company directly. And then contact the Medicare agency directly. Because website backend development.
Honestly I've been trying not to get too spun up about the media coverage of healthcare.gov, but in this case, I was powerless before the awesomeness of Talking Points Memo's deployment of stock photography on this random AP wire story.