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Theoretical Age Related Risk of Chromosome Abnormality in Multiple Gestation*
The calculator below calculates the theoretical risk for Down syndrome and chromosome abnormalities in multiple gestations.*  At least for twin gestations, the theoretical risk may be an overestimate of the observed risk of Down syndrome in some populations [2,3].

Maternal Age (or age of eggs )                             

 

Down Syndrome

 All chromosomal aneuploidies

  One
 affected
One or both affected Both
 affected
One
  affected
One or
both affected
Both
 affected

Twin
One placenta
    1 in
    1 in

Twin
Two placentas
1 in
  1 in
  1 in
 
  1 in

Twin
Unknown # placentas
  1 in
 
    1 in
 

Triplet
Three placentas

1 in

         

Quadruplets
Four placentas

1 in

         
 

REFERENCES

* Calculated risks are based on midtrimester risk of chromosome abnormalities for
singletons as provided  by the California Department of Health Services Genetic   Disease Branch

1. Matias A,et al .Down syndrome screening in multiple pregnancies. Obstet Gynecol Clin North Am. 2005;32(1):81-96 PUBMED
2. Jamar M, et al. A low rate of trisomy 21 in twin-pregnancies: a cytogenetics retrospective study of 278 cases. Genet Couns. 2003;14:395-400.PUBMED
3. Cuckle H. Down's syndrome screening in twins.J Med Screen. 1998;5(1):3-4.PUBMED
 

Created: 11/2/2005


 

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