If you were in their position you would be wise to announce the pregnancy as late as possible and suggest a due date later than reality to avoid the "when's it due?" speculation ramping up. By saying it was a spring baby a lot of people have been expecting it since early March.
The problem they've created for themselves is announcing it ridiculously early for no good reason. She hasn't had hyperemesis and she didn't cancel her visits to Zika-risk areas so there was no reason at all to announce it when they did. A non-existent or barely- there bump can easily be disguised and they're not short of money for well-tailored clothes.
I'd say that they announced early because they were over-excited rather than attention-seeking, but the indiscretion of her friends may have led them to believe it was better for them to announce it rather than someone mentioning it on a chat show.