Are scans accurate?

[MumOfHals]

How accurate are growth scans?

Had a scan last week for a 4D scan and babies head was measuring at 288mm at 28 weeks - 98th percentile

Had a NHS fetal medicine scan today and was measuring 281.9mm at 29 weeks - 60th percentile

So confused, surely the head can’t shrink?

Who did the 4D scan? Personally I would be more inclined to lean towards the NHS scan compared to a 3rd party.

A private scanning clinic x

I’d trust the NHS one

Private clinics aren't regulated. NHS trusts have image audits to ensure sonographers are measuring the correct cross sections of each structure.
However even with a good quality scan, the predicted measurements can be 10-20% inaccurate.