MadSci Network: Genetics
Query:

Re: What is the probability of a woman having twins more than once?

Date: Wed May 24 14:20:24 2000
Posted By: Joshua McElwee, Grad student, Molecular and Cellular Biology, University of Washington-Seattle
Area of science: Genetics
ID: 959042463.Ge
Message:

   Hi John.  A quick internet search turned up this site:
 http://www.babydata.com/info/docs/info/7com/twin_pregnancy.htm

  and this information:

The chance of monozygotic twinning is about 3-5/1000 births worldwide
The chance of dizygotic twinning is about 1-50/1000 births.

  If we take a rough average of these two types of twinning..say 10/1000, we 
can figure out what the chances are of a woman having sets of twins more 
than once.  Because the chances of having multiple sets of twins are 
independent of each other, (that is, having one set of twins doesn't affect 
the chance of having another set of twins,) we use what is called the 
"product rule" to determine the chance of having multiple sets of twins.  
All we have to do is multiply the probability of having twins once (10/1000) 
times the chance of having them again. (10/1000)  So..

10/1000= .01

.01*.01= 1/10000

   There is a one in 10000 chance of having two sets of twins, assuming that 
nothing else influences those chances.  

   As you'll see in the web page above, though, there are other factors that 
influence the chances of having twins.  Heredity, the age of the mother, the 
concentration of hormones in the mother, fertility drugs, and other things 
can all affect the chances of having twins.  Hope this has helped.



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