My baby's age on the scan report is different to my stage of pregnancy. What does this mean?

You should have a dating scan done during your first trimester has an accuracy of +/- 5 days. Doing it in your second trimester has an accuracy of +/- 2 weeks. It is important to see the doctor early to do the dating scan. From your menstrual cycle we can calculate the estimated due date, which will be deemed accurate if it differs from the dating scan by +/- 1 week. Using your menstrual cycle to calculate your due date only works if you have a regular menstrual cycle.