Maternal Age (or age of eggs )
 
 
 
 

Down Syndrome

 All chromosomal aneuploidies

  One affected One or both affected Both affectedOne affectedOne or both affectedBoth affected
Twin One placenta     1 in
    1 in
 
TwinTwo 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