Read the web page on Dr. Maria New (Cornell University).  Don’t worry and it is not such a scary thing. The dex dosage is very low.

I had the CVS testing and stopped the dosage at 10 or 12 weeks.  I had ultrasounds at 8 weeks and at the CVS testing at 10 weeks.   No ill effects from the dex. My children are 10, 5, and 2 (boys).  The 10 and 5 year have salt wasting CAH.  The 2 year old does not have CAH.  You can stop the dex treatment if it is a boy. The CVS test is better because you can have it done at 10 weeks and the sex can be known within 48 hours. The CAH testing takes longer - 2 weeks but at least you can stop the dex if it is a boy.