Increased risk of having child with DS after having had a child with DS?

[glimmer]

I have read several times, that after having had a child with DS (or other chromosomal disorder), one is at an increased risk of having another, even if the genetic disorder is 'de novo' and not inherited. When 'increased' I mean higher than other mothers in the same age range.

Can anybody explain me why this is or point me to literature or links?

Thanks.

With DS specifically, the thinking is a degeneration of the ovum over time is the issue and people don't all age in exactly the same manner.

hi,
Our geneticist explained it very clearly but I cannot remember the exact words - we were told one DS pregnancy gave us a risk of 1:100 (excluding age associated risk), despite going on to have an unaffected pregnancy next time, our next (Edwards syndrome) pregnancy brought our future risk to 1:50. If it had been another DS pregnancy we would have been more like 1:25.

Incidentally the risks were calculated on my husband and I together (neither genetic 'carriers' of any condition) having another affected pregnancy, and on the probability that the T21 & T18 pregnancies being caused by either a dodgy sperm or a dodgy egg, so neither of us knows who is to blame as it were.

Not a straightforward answer, but I think genetics is a bit like that when it comes to non-inherited conditions.

Thanks for your answers. I have to admit that I don't fully understand them but I get the idea....

They gave me a recurrance risk of 1:100,
although the risk for the genetic disorder I am interested in is 1: 200 000 000, which means my risk for having a pregnancy with this condition is increased
by a factor of 2 million !!! I thought that's sort of crazy given the rarity....

But I think it's more along the lines of picking a number that's small but not non-negligible...

Babylily - so sorry you had two pregnancies
with chromosomal disorder. Life is just not fair.

To be honest having been through the same ourselves, having a clear genetic screen and yet being told our inherent risk is higher because of a previous DS pregnancy, I think that the issue is probably more genetic elements to trisomies that are not yet understood.

Hi I had a baby (stillborn sadly) with a de novo disorder (much rarer than downs) and I was early 20s at conception. I have 5 living children with no genetic problems and also lost another stillborn who had no problems, she was just too premature to survive. I think it is very unusual to repeat if the parents are not carriers of a disorder/translocation but it does happen rarely.