A dating ultrasound or dating scan is a scan done early in pregnancy (before 12 weeks). It is usually done to check how many weeks pregnant you are and therefore to calculate the estimated due date, but it can be done for other reasons. Only a few women need a dating scan.

How early can you do a dating ultrasound?

Dating ultrasounds are most accurate when they happen between 7-12 weeks, and are calculated by measuring the fetus crown-rump length. This generally predicts the expected date of birth within 5 days.