Does my employer need to honor my doctor's restrictions for me while pregnant?

The issue is how disruptive are the restrictions, or how core are the things you cannot do to your job. Employers are enjoined from discriminating against women due to pregnancy. Not discriminating means making reasonable accomodations. A "reasonable accomodation" is one which does not cost too much money and/or is not too disruptive to the employer. If the requested accomodation requires that the employee be placed in a different job than the one she was hired to do, and/or makes it effectively impossible to do her job without undue disruption, the employer may not have to honor the requested restriction.

Thus, the specific facts of the job and the requested accomodation are critical to answering your question. Since the issue is so fact-specific, you should meet with an employment law attorney, who can evaluate the situation in detail.