Why might your baby's ultrasound show he had fluid in the neck?

I think you had a nuchal scan, done at around 12 weeks. This measures the fluid at the back of the neck and MAY, only MAY be an indication of Down's syndrome. You will probably be offered an amniocentesis which will give a diagnosis. A friend of mine had twins, both of whom had positive signs. She had a double amnio, both of which were negative and her babies are fine, (now about 1 year old)