Hi there.
Long time away from BB but remember looking everywhere for a decent pre-natal yoga workout ... found Shiva Rea's "Prenatal Yoga" DVD to be really good for all stages of pregnancy with modifications for each trimester demonstrated by ladies at each stage (though the relaxation section could go for longer...). Apparently there's a follow up Post-Natal workout too but haven't used that (yet). Can sometimes find these on Ebay if that's any help. Agree that the Pilates TV Pregnancy DVD is terrible... a lot of the positions/exercises are exactly what you shouldn't be doing.
Hope this helps.
Tam