Accurate dating scans conception date

I would like to know the accuracy of ultrasounds in the first trimester. On Feb 2 I went off birth control for good & had withdrawal bleed on Feb 5-8. He used a condom, I believe I was on birth control (but cant remember for sure), and took Plan B 55 hours later.Other ultrasounds at 19, 21, and 27 weeks all gave EDD of 11/12. Totally 6 ultrasounds have all given you the same EDD - 11/12.

Having a scan in the first few months of pregnancy can be a thrilling experience.It's amazing to see the little blob with a heartbeat that will soon become your baby.I can give an "estimate" but I really don't know because I never keep track.(Plus I have always been told that because of metabolic issues, and PCOS that it would be very hard for me to get pregnant).Could the birth control not have worked in Jan, the embryo lived through the withdrawal bleeding, and the fetus has continued to measure small throughout the pregnancy? According to this period date, the most likely date of conception would be around 14 days after the period, that is around the 19th of February.

Ultrasound has intrinsic error of upto maximum 5 - 7 days, so the probable dates of sex would have been a week before or after the 19th of February, but in NO WAY as early as January 18th.Your midwife may recommend an early scan at between six weeks and 10 weeks if you have experienced bleeding.You may also be offered an early scan if you've had a previous miscarriage.Does anyone know which is actually more accurate: going by your last missed period or if you truly know your conception date to figure out your due date?I know doctors 99% of the time go by lmp but my conception date would make my due date 6 days earlier.I didn't think anything of it, because I am almost 38, and this has never happened to me before.