Maternity Shopping

Rebecca • We're having baby #1!
Today I tried to shop for some maternity clothes at old navy for the first time. I didn't have time to try on, but I'm usually a large in old navy, so I got larges in maternity. I got home and they are all gigantic on me. What are the size rules when shopping for maternity clothes, especially for pant sizes? If I'm regularly a 16, will I be a 16 in maternity?