Genetic risk maternal age

Mother's Age and Risk of Having a Baby With a Chromosomal Abnormality

Age of Mother	Risk of Down Syndrome	Risk of Any Chromosomal Abnormality
20	1 in 1667	1 in 526
21	1 in 1667	1 in 526
22	1 in 1429	1 in 500
23	1 in 1429	1 in 500
24	1 in 1250	1 in 476
25	1 in 1250	1 in 476
26	1 in 1176	1 in 476
27	1 in 1111	1 in 455
28	1 in 1053	1 in 435
29	1 in 1000	1 in 417
30	1 in 952	1 in 384
31	1 in 909	1 in 384
32	1 in 769	1 in 323
33	1 in 625	1 in 286
34	1 in 500	1 in 238
35	1 in 385	1 in 192
36	1 in 294	1 in 156
37	1 in 227	1 in 127
38	1 in 175	1 in 102
39	1 in 137	1 in 83
40	1 in 106	1 in 66
41	1 in 82	1 in 53
42	1 in 64	1 in 42
43	1 in 50	1 in 33
44	1 in 38	1 in 26
45	1 in 30	1 in 21
46	1 in 23	1 in 16
47	1 in 18	1 in 13
48	1 in 14	1 in 10
49	1 in 11	1 in 8

Table References: Hook EB. Rates of chromosome abnormalities at different maternal ages. Obstetrics and Gynecology 58:282-285, 1981 (Data USA sourced)

Hook EB, Cross PK, Schreinemachers DM.Chromosomal abnormality rates at amniocentesis and in live-born infants. JAMA. 1983 Apr 15;249(15):2034-8.

Schreinemachers DM, Cross PK, Hook EB. Rates of trisomies 21, 18, 13 and other chromosome abnormalities in about 20 000 prenatal studies compared with estimated rates in live births. Hum Genet. 1982;61(4):318-24.