Anatomy scan before 20 weeks?

Lila • 🕉Writer, biker, researcher and world traveler! 💻🏍📑🗺 Twin boys due soon! 👶👶

I'm expecting twins and I'll be 18 weeks two days when I have the anatomy scan done, but I was under the impression that this happened at 20 weeks. I guess it's halfway for twins but I wanted to get an idea.

Thanks in advance 🙂