Hi, I'm a student genetic counsellor. The information provided by Rosalie on recurrence risk of CAH is incorrect.CAH is a recessive genetic disease. This means if both parents are carriers each pregnancy has a one in four (25%) chance of being a CAH baby.
I'll explain why. We all have 2 copies of every gene in our cells, one which has come from our mother and one which has come from our father. So we all have 2 copies of the CAH gene. In some people one copy of the gene is normal, while the other copy is faulty. These people are called carriers. They are not affected by CAH themselves but they can pass the faulty gene onto their children.
Only people who have two faulty copies of the gene are affected by CAH.
To be affected by CAH a child must inherit one faulty copy of the gene from their mother and another from their father.
Carriers will pass on their working copy of the gene half the time, and their faulty copy the other half of the time, so the chance of BOTH parents passing on a faulty copy of the gene is 1/2 times 1/2 = 1/4 = 25%
If only one parent is a carrier then none of their children will have CAH. Since the parent who is not a carrier cannot pass a faulty gene on, children are at no risk of inheriting two faulty copies of the gene. In this case 50% of children (on average) will be carriers, and 50% will be 'normal' i.e have two working copies of the gene.
Rosalie is right about each pregnancy having the same risk, regardless of how many CAH children you have already had.
If you want to know if you are a carrier or not, seeing GHSV (or any other genetic health service) is a great idea. If you turn out not to be a carrier you have nothing to worry about. P.S. somewhere around 1/50 people in the general population may be carriers of CAH.
