20 week appointment?

Court • 26 Weeks Pregnant with my Baby Boy💙

Hi girls... So I had my 20 week scan on Wednesday and today just received a letter saying to go to the hospital for an “antenatal clinic appointment” in just over a week (2 weeks after my original 2 week scan) Says appointment could last up to 3 hours.

Is this the normal for everyone? Does anyone know what this appointment would be for? Thank you!

(St Mary’s Hospital)