I am 22 weeks pregnant and had the CVS done at 12 weeks.  They too were unable to get any cells because of the same reason.  We were really shaken up that we had done unnecessary harm to our baby and they weren’t able to get anything.  The chance of miscarrying really scared me because I miscarried this summer.  We then had an ultrasound done at 14 weeks along and they were able to determine that we were having a boy.  We went back 2 weeks later for another ultrasound and again, boy.  Since CAH doesn’t affect a boy in womb, we weaned off the steriods and did not have an amnio.  There was no sense in doing another risky procedure when he will be tested at birth.  I am still seeing my perinatologist for another couple of visits.  Good luck with your pregnancy.  I too have gained alot of weight but I think since going off steriods it has slowed down (somewhat).