Are twins growing slower in early pregnancy than one baby?

J

I got to know 1hr ago I'm expecting twins!

Went to my scan at 5+4, saw 2 gestational sacs. But there was no yolk sac in either. With my first around this time there was a yolk sac.

I don't know if I should be concerned. My doc said it's everything in time, but I'm a very nervous mama. So please let me know your opinion! Thank you!