Down’s Syndrome and age of parents

It is an established fact that the older the mother, the higher the risk of a Down's syndrome pregnancy. Even though a Down's baby can be born to a mother of any age, the risk increases significantly above the age of thirty-five.

The risk to a mother aged twenty is about 1 in 1000, rising to 1 in 600 at 30 years, 1 in 250 at thirty-five and as high as 1 in 70 at forty. The risk is an extremely high 1 in 20 by the time the mother is 44. As can be seen, the risk rises almost fifty-fold at the age of 44 compared to the risk of a 20-year old mother.

Paternal age and Down’s Syndrome

There is no evidence that the father's age influences the risk of having a Down's syndrome baby in any way.

Other risk factors for Down’s Syndrome

One or the other parent may carry a potential chromosomal abnormality, even though the parent is normal. Through a complicated chromosome material swap (known as ‘translocation’ in medical language); the parent may produce gametes with extra chromosomal material. If this extra chromosome is on number 21, the resulting fetus will be Down's. If it is the father who is carrying the translocation, the risk of producing a Down's baby is one in ten (10%). If it is the mother who has the translocation, the risk is much higher at one in two (50%). This kind of risk is independent of the age of either parent.

About 2% of all Down’s syndrome cases are due to parental chromosomal translocation. When a Down's baby is born to a young mother, it may be worthwhile checking the chromosomes of the parents to establish whether one of them might be a carrier of a translocation. This will help in counseling regarding future pregnancies and estimation of risk of recurrence. The carrier parent will have no telltale features of any kind and is otherwise perfectly healthy.

Risk of recurrence of Down’s syndrome

Except for those carrying a translocation, a mother who had a Down's pregnancy has a risk of this recurring increased three-fold compared to the average. This means, if the mother is going to be 30 years old at her next pregnancy, while the average risk is 1 in 600 at this age, her risk will be significantly higher at 1 in 200.

Screening tests for Down's syndrome

Any woman who has been pregnant will be aware of the terms "triple test" or "double test". These are the commonest test employed for screening.

What the triple test really means is that a small sample of blood taken from the mother is checked for three (hence "triple") different hormones produced by the fetus or placenta. The levels are computed, together with other important factors such as maternal age, gestational age and previous history, to estimate the risk in that particular pregnancy. In the double test, only two of the hormones are checked.

The sensitivity of the "double" test in detecting an affected baby is similar to that of the "triple" test. Maternity units tend to adopt one or the other.

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