My sister was about 3.5 months pregnant when she was looking for and got a new job. Yay for her! Like you, that meant that she would be at the company less than a year by the time she'd be giving birth, so therefore no FMLA guarantees. On top of that, this was her first job since getting into the new industry with a new Assoc Degree, so it's not like she had some stellar work experience that would make it easier to get another job if she needed to.
During the interview and offer process, she did inform them that she was pregnant. They hired her anyway because there's more to her than just being pregnant. In this economy, your company hired you because they wanted YOU. There are plenty of other people looking for jobs that would likely be qualified, but they picked YOU because you met their needs and fit in with their plans better than anyone else!!
My sister ended up taking about 5.5 weeks of leave after giving birth because it was unpaid and she didn't want to give her boss any issues since FMLA didn't apply to protect her job. She had an uncomlicated birth, so that helped her get back on her feet quickly. All is well and she's still employed :) and I get the joy of babysitting her now-5-month old every day!
So for you:
1) tell your boss as soon as you are comfortable with this pregnancy (given your history)--they can't fire you for being pregnant! But that also means you need to have an open and honest dialogue with your manager...you can talk about your fears, etc. Let him/her reassure you that they hired you for you! But you need to reassure them that you are committed to them! Everyone needs a warm and fuzzy feeling coming out of this.
2) after that, work with your boss and HR department on a reasonable amount of time that will be acceptable for you to be out on leave--perhaps there is an agreement document of some sort that you all could sign after you come to an agreement that would essentially serve the same purpose of the FMLA job protections. 6 weeks of unpaid leave is the FMLA minimum.
3) CONGRATULATIONS on being pregnant! Try not to stress. No matter what, it will all work out.