Sleepysue, It's a test they've started doing in the last few years, the combined test works out the risk factor using blood test, mum's age and a measurement at the back of the babies neck. If your risk comes back as high you then have the option of amniocentesis or another invasive test if you choose.
The advantage is they can do it between 11 - 13 1/2 wks which is earlier than the amnio can be done.
I'm sure I read somewhere that NHS now have to offer it to everyone. That's really bad your hospital dont do it Ceris - hope it all goes ok xxx