How to tell your new job you're pregnant

I just started a job a few months ago and I also happen to be 3 months pregnant. I found out that I was pregnant after they made me an offer but accepted anyway. Have any of you experienced starting a new job while pregnant? How and when would you recommend that I notify them? Also who should I notify, my manager, my union rep or HR? For context, I'm in California  and I'm not sure if FMLA or California's equivalent will apply to me since I will not have been on the job for 1 year. But, I'm counting on the fact that my job is unionized to help me a bit in negotiation. Let me know what you think.