Did they really announce her pregnancy that early?
Her "close friend spilled the beans" on that date.
See here
The official announcement came in on 8 September, which, even if we disregard the former "beans spill" date, still means they formally announced the pregnancy when she was only around seven weeks pregnant. Who formally announces a pregnancy when they are only seven weeks pregnant? Even if you have an early scan, you are not necessarily guaranteed a heartbeat at that GA.
Interestingly, if the latter date is legit, then the beans spillage date would be approximately the date of conception ... which seems rather coincidental to me.
To be fair, if I were them, I would muddy the waters a bit. If I had their resources and cash, there is no way I would give birth in a hospital with all those crowds and TV crews outside -- look what happened last time with that nurse, for example. What I would do is give birth at home or elsewhere, and then do a media/PR presentation at the hospital at a later date. It would be safer and far less stressful.
Plus ... a couple of US mags have already reported that she has had the baby and it is a girl. 