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Current, Basic and Advanced Information about genetics DNA structure
The George Washington University Medical Center

Risks

Risk of Having a Live-Born Child with Chromosomal Abnormalities

Maternal Age
Down Syndrome
All 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
1/384
32
1/725
1/322
33
1/592
1/285
34
1/465
1/243
35
1/365
1/178
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

Data from Hook and Chambers (1977) and Hook (1981).
Because sample size for some intervals is relatively small, 95-percent confidence limits are sometimes relatively large. Nonetheless, these figures are suitable for genetic counseling.

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