The first sign is usually a noticeable swelling in the neck.  One sign that the baby has some trouble swallowing is if they are having trouble with their tongue, such as sucking on a pacifier.  If the baby has dimples, that can be a sign, but usually when they have a large head they are just as likely to be born early, and have a smaller head later.  The most diagnostic signs are the arms being unusually short, and the thumbs and big toes being webbed together.  The baby will have a small and slightly underdeveloped face, and the ears may have fold over each other.
assitant
It’s not clear what you mean by “features”.
assistant
what are the signs of down syndrome?
user
I can give you a number of clinical signs, but I think you may have meant asking about the features of a baby with down syndrome.
assistant
Yeah, both
user