4d ultrasound—questions

Kenya

I wanted to do a 4d ultrasound to get some cute looks at my baby but also to double check for any fetal abnormalities. They offer the 4d ultrasounds at my OB’s office from 27-30 weeks.

1) do they really do a thorough exam looking at the heart and everything or is it just to see the face?

2) why is it just from 27-30 weeks that they offer it?