Maternal Age and Risk of Down Syndrome

Maternal Age

Down Syndrome Risk

All Chromosome Abnormalities Except 47, XXX

20

1/1923

1/526

21

1/1695

1/526

22

1/1538

1/500

23

1/1408

1/500

24

1/1299

1/476

25

1/1205

1/476

26

1/1124

1/478

27

1/1053

1/455

28

1/990

1/435

29

1/935

1/417

30

1/885

1/384

31

1/826

1/322

32

1/725

1/285

33

1/592

1/243

34

1/465

1/178

35

1/365

1/149

36

1/287

1/149

37

1/225

1/123

38

1/177

1/105

39

1/139

1/80

40

1/109

1/63

41

1/85

1/48

42

1/67

1/39

43

1/53

1/31

44

1/41

1/24

45

1/32

1/18

46

1/25

1/15

47

1/20

1/11

48

1/16

1/8

49

1/12

1/7

References

(1) Hook, E. and Chambers, G.M., Birth Defects 13 (3a): 123, 1977.
(2) Hook, E., Obstetrics and Gynecology, 58: 282, 1981.
(3) Ferguson-Smith, M., and Yates, R., Prenatal Diagnosis, 4: 5, 1984.  

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