from the june ddc, but just wanted to add my personal experience: with #1 and #2, never took any. with #3, took it from 37 weeks orally, 1000 mg daily. then did a few vaginal applications after term.
with the first two i only effaced a bit prior to actual labor, with dd i was 80% effaced and several cm, and very stretchy. this time, i have been lax in my epo-taking and am paying for it with a lovely rigid cervix...i am a bit dilated and 50% effaced...but i know with dd it was much more soft.