36 weeks and already dilated

Went to the doctors today because I started bleeding last night (I'm 36 weeks today) and having Braxton hicks contractions. Doctor did a pelvic exam and said I'm 2cm dilated, 80% effaced, and that my little guy was already at -1. So I'm resting up per doctors orders. Just wondering if anyone else experienced this before and how long before you actually delivered? Doctor wants the baby to stay in there at least until 37 weeks.