Patient's question:
NoDoctor's answer:
It's not easy to determine, and calculations often result in some error compared to the child's actual size. For your situation, I recommend that you do a regular black and white ultrasound to check the gestational age about one month before the screening. This way, you can go at a more accurate time. If it hasn't reached 22 weeks by then, I suggest you can book a later appointment. If it has reached 22 weeks, then you can proceed with it.