Thanks Phoebe.
The doctor also says we can only wait for now and that the final
diagnosis can be done probably aroud 12 weeks.
However, I read an article that says that if the mass is larger than 7
mm in diameter, the diagnosis can be made earlier as they have never
seen a physiological midgut herniation go away when it's so big (the
physiological midgut herniation is the normal part of the embryo
development for which the intestines get out of the tummy, rotate and
then go back in by 12 weeks). So that's what is really worrying me,
that it's so big. Plus, the doctor seemed really concerned.

Pleae let me know if there is someone who has seen this and then it
disappeared.