When I was pregnant with my son, I knew the first day of my last period (It was the night I went to a concert and I was really bummed about it). I knew the day I had sex (Only had sex once that month and it was on my-then-boyfriend-now-husbands 1 year anniversary with me). When through my entire pregnancy knowing my due date was October 28th.
Through the whole pregnancy I always measured small - 2 or 3 weeks small. I'm a small person to begin with so my doctor wasn't too concerned until week 28, and then I had to have ultrasounds every two weeks just to make sure everything was still going good.
Well, I had my 40 week check up on October 27th. I was miserable being pregnant so my doctor decided to schedule an induction for the following Monday, November 1st.
As my doctor was looking through my records she came across the very first ultrasound I had at 11 weeks, and apparently the technician noted then that the baby only measured 9 weeks and switched my due to November 11... But nobody told me! So the whole pregnancy I thought my due date was October 28 only to find out at 40 weeks that my due date was November 11 and I was only 38 weeks. That is probably the cruelest joke you could ever play on a pregnant woman.
Since I was 100% positive on my dates (I still believe I was 40 weeks), and even 38 weeks would still be in the safe zone, my doctor scheduled an induction for November 1.
I went into labor on my own on October 29 and now have a beautiful 2 year old son. He was born at 6lbs 12oz and 19 inches long so he wasn't tiny. Just a small baby for a small mommy :)