Idk if there is a difference due to it being federal jury duty, but PA title 42, chapter 45, section 4503, a.8 lists "breastfeeding women who request to be excused" as exempt from jury duty. You may have to make the request in writing.

I am not a lawyer.

https://www.legis.state.pa.us/WU01/LI/LI/CT/HTM/42/00.045.003.000..HTM