Appt with New Doctor

I’ve decided this time to go with a new Midwife.  Not because I didn’t like the old one– she actually suggested that I switch to this one– because it would be much less expensive and we are paying for everything ourselves this time since we have a ridiculously high deductible.   She sees clients in her home for most of the pregnancy. However, before you see her you first have to go see the doctor or nurse practitioner at their office.  I think basically they are trying to screen you to make sure you aren’t high risk before you see the midwife.  Everything went well but I think the nurse practitioner could tell I was a little nervous and so she gave me a free ultrasound so I could see the baby’s heartbeat.  The heartbeat looked great, but one thing has continued to bother me through both ultrasounds. The baby is measuring about four days behind the day I’m positive we conceived.  I know that its hard to tell, and difficult to measure, blah, blah, blah, but the due date keeps coming up Dec. 25 when I know it should be Dec. 21!  Neither doctor seems concered, just me.  I was just wondering if anyone else has experience with ultrasound measurements that were off, or has any words of advice.  Last time Jack always measured a few days ahead.  I guess I just always like to have something to worry about!