Sitting in an uncomfortable wooden chair for eight hours is hard enough. Doing it while eight months pregnant or needing to pump breast milk is nearly impossible.
In recent years, the law has caught up to reality. Today, over 20 states (including California, Illinois, and New York) have specific laws that allow nursing mothers to be automatically postponed or entirely excused from jury service. You usually just need to provide a doctor's note or sign an affidavit stating you are currently lactating.
Being pregnant is not an automatic exemption in most states unless you are very close to your due date. However, if you are experiencing a high-risk pregnancy, severe morning sickness, or your doctor has placed you on bed rest, you easily qualify for a standard medical exemption. Have your OB-GYN write a letter to the court.
If you choose to serve while nursing, courts are federally required to provide 'reasonable accommodations.' This usually means providing a private room (that is not a bathroom) for you to pump, and allowing you extra breaks. However, older courthouses are notorious for ignoring this rule. Call the jury clerk ahead of time to confirm a lactation room actually exists.
Nursing mothers can be automatically excused in many states. If you are pregnant and experiencing complications, obtain a standard medical excuse from your OB-GYN.