Thanks to scientific research we know that certain substances or circumstances may cause alterations of embryonic development, resulting in birth defects in the future baby.The agents that can alter the development of the embryo and fetus are considered risk factors. But to understand the meaning of the term "risk" is not simple. In fact, it is relatively common that some people deem as an overstatement considering the substances or adverse circumstances for the baby.
Even trying to document the overstatement with comments (which are very harmful) as: "I know a woman who, 42 years old, has had a healthy boy and beautiful" or "A friend had rubella during pregnancy and had a healthy child ".
The advanced maternal age and suffered rubella during pregnancy are important risk factors, which does not mean that all women who suffer from mature or rubella during pregnancy are to have a baby with abnormalities.
No agent, a side that is, causes birth defects in all the children of all women exposed to it.
What we mean when we talk about risk factor is that among pregnant women who come into contact with any of those factors will have a larger proportion (which is different for each factor) of children with birth defects among the group Women who were not in touch with these actors.
Statistics
For example, according to some statistics, the frequency of children with Down syndrome among mothers under 35 years is 0.72 per thousand boys born, while among women over 35 years is 7.54 per thousand. That is, they have ten times more risk of having children with Down syndrome than the younger ones.
When we say that the maternal age is a risk factor, we are not ensuring that all women over 35 years will have children with Down syndrome. The same applies to infections during pregnancy, alcohol, to snuff, contact with animals ... The problem is that we can not know who is going to affect a particular agent and who is not.
