Down's statistics question

excited16

I've been trying to find info about what exactly the statistics for Trisomy 21 (downs) mean.  I've found quite a bit of conflicting information.  For example at age 40 does the 1/100 statistic mean the chance of conceiving an embryo with Down's (though many will miscarry early) or does the statistic mean those that are carried to term +/- those who choose to terminate the pregnancy...

Confusing.