Chance of Down's syndrome 2nd child...confused.?


I am confused about something. First, all medical professionals say Down's syndrome is NOT genetic....it is a unsystematic occurrence.
The chance of having a DS tot is estimated at 1 in 800 as an average over all age groups.
So then, WHY do the likelihood of having a 2nd child with DS jump to 1 surrounded by 100?? It doesn't make sense.....one would think the chances are LOWER since it is a variable event.
Just curious but confused..
Answers:
The docs/statistics are correct.....for the average aged child-bearing population. The chances are around 1 in 800.

As a woman ages so do her eggs and this is why the statistic seems to be confusing. As the eggs age the RNA also starts to undergo some changes. This is especially true with women over aged 40 and the risks of a genetic deterioration occurring increases makedly once she is over age 45.

Each pregnancy is approaching a flip of the coin. Just because the first flip turned up heads it doesn't indicate in any way what will turn up on the subsequent flip.
But, if the first pregnancy produced a Down's Syndrome offspring then the risks of the next pregnancy doing impossible to tell apart is significantly higher because there is obviously a difficult chance ALL the remaining eggs may also be so affected. It doesn't mean that purely because the first pregnancy produced a Down's that the second pregnancy will also produce another Down's but the chances are much higher. Add to this that if the first pregnancy occurred within an older woman then the second pregnancy would be occurring in an even elder woman whose eggs are that much more degraded by time.

There are several other birth defects/conditions which rise with age but Down's seems to be the most common 'older egg' scenario. Just so you don't have an idea that women are alone in this, a males sperm also starts to show signs of ageing and can deteriorate causing pregnancy problems too but not to as great an extent as the females eggs.

Just in shield you didn't know: a woman is born with many times more eggs than she'll ever need contained by her entire life. It's only at puberty do these actually develop into proper eggs in position for maturation and fertilisation. You never make any new eggs after you're born.

Hope this cleared things a little for you.
This is in actuality a simple one. It's because your risk increases with age, and, by definition, women who are having their second child are older. That's adjectives there is to it. Source(s): http://www.vhemt.org/biobreed.htm#babies


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