Is it possible to have missed a ds diagnosis at birth.. my daughter is 2 and has the signs physically and mentally but they are only looking at autism?

Possibly: Down syndrome is usually recognized easily by pediatricians & those working with the developmentally delayed. Features are usually distinctive. However, there are rare mosaic ds kids or kids with a variety of very tiny chromosomal defects that are not identified unless you look. High resolution chromosome studies can identify some less common causes of distinctive physical features.

Unlikely: Patients wth down's have farily classic features that would not likely be missed if they had been seen by a medical provider. Screening for down's is also part of routine prenatal care unless the parent opts out of those tests. Both medical conditions involve developmental delay and both can have a range of functional levels. You should ask your provider for the specific reasons for autism dx.