Has anyone else had this experience


Is anyone else pretty sure about there conception date ( I mean tracking by basal temp, opk’s, the whole nine) but baby is measured a week later than you are far along. At my last appointment I was 10 weeks 2 days but measured 9weeks 2 days. I know my little one may be small due to how tiny I am and was at conception and due to my health (lupus etc.) but I was wondering if that has happened with anyone who doesn’t have health issues...?