Was there any reason given for the complications? Downs usually happens because of the egg's age (which is why it is related to the age of the mother -- we have all the eggs we're going to get, when we're born). Did the doctor say this would be related to your age? If not, talk to the doctor and ask your questions, he or she should be able to help you.
I had another type of mutation with my 3rd pregnancy. I am currently pregnant again and saw the genetic counsel. They explained the possibility and percentages of similar thing happening again. I suggest you see your counsel (you probably saw one with your previous pregnancy). I am also due for CVS testing which can only be done during certain time in 1st tirmester. The test can answer the questions you have.
100% Agree with Annie. But there are also blood tests that can be completed as early as 10 weeks to determine the likelyhood that your baby may again be born with Down Syndrome. There is also a sonogram that is done around 11-13 weeks that will check the back of the baby's neck (skin) which can also tell usually with an 85% accuracy if the baby will have Downs.
I am so sorry for your loss, but if it helps to put your mind at ease please do consider the testing.