12 week scan measuring behind

[ChildOfTheMoon]

Had my first nhs scan today. I'm 13 weeks but baby is measuring 5 days behind. Wondering if this is normal.
I've had 2 previous scans and each time baby was only 1 day behind.
I know my gestation date exactly as we had ivf
Found it difficult to communicate with doctor as his English wasn't great

It's very normal, the further into your pregnancy you are the less accurate the scan dates become - we are all individuals who grow different shapes and sizes and at different rates and this is particularly true of babies. 5 days is really nothing to worry about.