Most states protect women that are in a job when they are pregnant and need to allow them the arrangements necessary for their appointments, birth, and even in some states PFL which is paid family leave after giving birth. Go to the HR department of your job if you cant speak to a supervisor or the supervisors supervisor and they should be able to direct you more in the abilities you have and your rights as a pregnanant woman in the workplace.

I'd suggest you set up a one-on-one conversation with your manager and just come out with it. Tell him/her that you're pregnant and (this is important) you want to work with him/her to schedule your appointments so that there is as little business interruption as possible. Employers can't fire you for being pregnant, but they CAN fire you if you can't do your job (for whatever reason, including absences). Before your meeting, think of options that would be attractive to the company - can you come in early or work late to make up the work/hours? can you work weekends? Try to put yourself in your manager's shoes and figure out how to make it easy for them to say 'yes.'

Good luck! Let us know how that conversation goes.

No one can fire you for being pregnant it's forbidden. You should let your employer know so that they can work with you on your schedule but also so they can plan for your absences. Again can't fire you for a pregnancy and you want to keep an honest relationship. Hope this helps