About Down syndrome (one or more correct answers):
It most often results from a maternal meiotic accident
When it is associated with a chromosomal formula 46,xx,der(14;21),+21, it does not require a family investigation
Its postnatal diagnosis can be confirmed quickly by molecular biology
Its risk of recurrence is close to 1/100 to 1/200 for a couple who have had a first affected child.
Its risk is reduced by advanced maternal age at the time of conception