I told mine at 6 weeks when we found out.

I asked to speak to the owner and my Chef and told them that I was about 6 weeks pregnant, and how did they want to handle it. (I had only been working there 4 weeks, and was hired as a long term prospect, unaware I was pregnant, so it was a big shock to them as well and disruptive of their business plans)

Anyway, I would have told them so early anyway as it really does affect the way I can perform my job (chef). So it meant everyone knew what was going on, and as I worked 6 days a week, 16 hour days, meant they knew why I needed time off for appointments etc.

I would be seriously considering the way you worded "I will be needing maternity leave this year because I am pregnant"... not sure of your personal situation, what is included in your contract/award etc, but if someone told me they were pregnant like that I would find it exceptionally rude.