Need some clarity on accuracy of early US

[coco894]

So, first off my period are 10 days late, so my cycle is not 28 days like normal people. So My period started December 4th ended December 10th I had sex with a guy on the 14th then got of course back with my bf which I hadnt been with since November on Dec 17th havent been with anyone else since. Found out I was pregnant January 19th they said I was 5 weeks 3 days with a conception day of December 26th my HCG levels were 3121 that day as well. They were concerned with the dates LMC or the fact there was no fetal pole yet, just a sac. So my question is should I be worried that conception could be 12 days off. Baby is 31 weeks and is actually measuring small, but i am small and only weighed 5lbs and 14 ounces when I was born. She is still, they say 31 weeks and not expected early. Could they still be wrong or should I really not worry. The Dr said early USs are usually 24 hours off if they are especially a 5 week one. Still messes with me. DNA test are too expensive.

[AnnieBrooke]

I agree with the doctor's estimate that you conceived around December 26, if your ultrasound on January 19 said you were 5 weeks 3 days.  That would be consistent with a longer cycle length.