Let's be honest: She is working this. Her makeup and hair are so perfect that I don't even miss a necklace, although a pop of color there might've been nifty. It's not a demerit that she skipped that, though. She had to know this was her night, and I think it shows a lot of maturity that she picked something that was classy without being showy, and which she'll be proud to look back on in ten years when she glances up at the framed photos on her home office wall/above the mantel/in her third downstairs half-bath.
In motion, when she turned sideways, there was a LOT of structure there that looked natural on a person that slim, but which also provided a wee security blanket just in case anybody decided to bring a fetus to the party. Just saying. WE do not think she looks in any way large; we are just responding to the Twitter speculation.
See? She's not filling out the extra space, but it's THERE, which is totally something a teeny-tiny person would want as a crutch if they were self-conscious about what they think their stomach is maybe going to do. So while I'm not sure yet if the rumors have merit, I can understand why they started.

"Hold it together Anne. Don't puke. Don't puke. Oyster crackers are ten minutes away."
I mean, if the girl is pregnant, she's the kind of pregnant EVERYONE wishes they could be. Which is to say, MAYBE it looks like she ate an extra olive? MAYBE? Frankly I think she looks great in this cute beaded dress.

This could just be layered over there because it's been chilly in Los Angeles.

... but this does kind of feel like the awards equivalent of sticking your actress behind a giant handbag and a potted plant.