Can chromosomal microarray detect down syndrome? what's the difference between chromosomal microarray and the conventional karyotypying?

It may, depends: First step is conventional karyotyping, if the clinical suspicion present for Down syndrome, detection of an extra chromosome 21, or trisomy, instead of two. In 95% of Down syndrome it's diagnostic, but If it didn't detect and suspicion is still there - next step could be a microarray, which designed to detect submicroscopic abnormalities not detected by regular karyotyping for the rest of 5% D-s