A.W.
I don't know if you've already told your employer, but I would wait until you are in the 12th week for security issues. Also, keep in mind that it is illegal for them to have asked if you were pregnant during the interview process. I would suggest sitting down with your direct supervisor and letting them know that you are pregnant, and it's a bit of a surprise, give them your health history, and let them know you are dedicated to your post until you are no longer capable of doing the job for health reasons.
You might be surprised at the support you could receive. I took a job at 7 months pregnant and was open and honest right from the start, and it's been a great partnership. Good luck!