Risk of chromosomal abnormality at age 35 is about 1 in 250. In the general population this risk is 1 in 1100.
Chromosomal disorders are associated with physical abnormalities and mental retardation. There is increased incidence in mothers of advanced age. The risk factor is about 1 in 350 at age 35 and 1 in 125 at age 45.
The incidence in 1 in 75 at age 50years. This should not be a cause of unnecessary worry for mothers of advanced age as even at age 50, out of every 25 women, 24 of the women will still escape chromosomal abnormality.