Thirty-five is the recommended age to begin amnio testing because that is the age at which the risk of carrying a fetus with such a defect roughly equals the risk of miscarriage caused by the procedure-about one in 200.
It is possible to perform an amnio as early as the 11th week, but this is not usually recommended because there appears to be an increased risk of miscarriage when done at this time.
The information provided by the amnio enables parents to make a decision regarding the need to terminate the pregnancy if it is believed that significant deformity is likely.
This is a very difficult decision to make, especially if the amnio was performed in the second trimester and you were looking forward to having a baby.
Negative results from an amnio analysis indicate that everything about the fetus appears normal and the pregnancy can continue without undue concern.