Down Syndrome Risk at 32: Understanding Causes & Testing

Question
I am 32 yrs of age and this is my first child. I had my menstrual on may 17th 2005. my question is down syndrome a heritity thing. I have passed up the test that test for that because I have been told that the test will come back positive when it is negative. My question to you is...
Is it really possible to have down syndrome when it doesnt run in the family? What really causes down syndrome?

Answer
The risk of Down's syndrome in a woman of 32 years of age is one in 2700 pregnancies. At the age of 35 it is one in 350 pregnancies. At the age of 40 it is one in 100 pregnancies. We usually do not test for Down's syndrome until you are 35 years old. Some women desire testing at an earlier age   and can do so if they wish. Amniocentesis is 100% accurate and does not come back positive when it is negative. An AlphaFetoProtein test is a blood test that does have some error and can have some "false positive" results. It is only 60% accurate for the diagnosis of Downs. If it comes back positive, we usually offer amniocentesis to make sure. Even if you have no children with Down's syndrome in the family, it is still possible if you are over 35 years of age. Down's Syndrome is caused by a "non-dysjunction" of chromosomes during meiosis. Although it runs in families, most of the time it is one time occurance.