Re: Downs

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• In reply to: William D. McIntosh, MD: "Re: Downs"

At Thu, 18 Feb 1999, William D. McIntosh, MD wrote: >
>At Thu, 18 Feb 1999, Barb wrote:
>>
>>After an extremely difficult pregnancy, the wife of one of our coworkers
>>recently delivered beautiful twin daughters; one of which has Downs
>>Syndrome. (Mom was 38, first pregnancy, opted not to have amnio.)
>>
>>Being a twin myself, my coworkers have wrongly assumed that I am an
>>expert on twins. Can you tell how common an occurrence this is, i.e.,
>>only one in a set of twins having Downs?
>
>This is not a very common occurence, but it does happen obviously. These
>must be fraternal twins, as identical twins have an identical genetic
>map. The risk of having a Down's syndome baby is about 1/100 for a
>woman of 38. At the same time, her risk of twins (assuming that she is
>not using any fertility agents) is around 1/70. Her risk of having one
>normal and one Down's baby would be 1/7000 births to women 38 years of
>age, I think. Math was never my best thing. In any event, the risk is
>very small, but not quite zero.
>
>--
>William D. McIntosh, MD
>Clarksville, TN
>
>This is for educational purposes only. It is not intended
> to replace consultation and examination by your physician
> or other health care provider.
>

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