Table 1 - Risk of trisomy 21 (Snijders et al. Ultrasound Obstet Gynecol 1999;13:167–70)

Gestational age

10 weeks

12 weeks

14 weeks

16 weeks

20 weeks

40 weeks

20
25
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45

1/983
1/870
1/576
1/500
1/424
1/352
1/287
1/229
1/180
1/140
1/108
1/82
1/62
1/47
1/35
1/26
1/20
1/15

1/1068
1/946
1/626
1/543
1/461
1/383
1/312
1/249
1/196
1/152
1/117
1/89
1/68
1/51
1/38
1/29
1/21
1/16

1/1140
1/1009
1/668
1/580
1/492
1/409
1/333
1/266
1/209
1/163
1/125
1/95
1/72
1/54
1/41
1/30
1/23
1/17

1/1200
1/1062
1/703
1/610
1/518
1/430
1/350
1/280
1/220
1/171
1/131
1/100
1/76
1/57
1/43
1/32
1/24
1/18

1/1295
1/1147
1/759
1/658
1/559
1/464
1/378
1/302
1/238
1/185
1/142
1/108
1/82
1/62
1/46
1/35
1/26
1/19

1/1527
1/1352
1/895
1/776
1/659
1/547
1/446
1/356
1/280
1/218
1/167
1/128
1/97
1/73
1/55
1/41
1/30
1/23

Table 2- Risk of trisomy 18 (Snijders et al. Fetal Diag Ther 1995;10:356–67)

Gestational age

10 weeks

12 weeks

14 weeks

16 weeks

20 weeks

40 weeks

20

25

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

1/1993

1/1765

1/1168

1/1014

1/860

1/715

1/582

1/465

1/366

1/284

1/218

1/167

1/126

1/95

1/71

1/53

1/40

1/2484

1/2200

1/1456

1/1263

1/1072

1/891

1/725

1/580

1/456

1/354

1/272

1/208

1/157

1/118

1/89

1/66

1/50

1/3015

1/2670

1/1766

1/1533

1/1301

1/1081

1/880

1/703

1/553

1/430

1/330

1/252

1/191

1/144

1/108

1/81

1/60

1/3590

1/3179

1/2103

1/1825

1/1549

1/1287

1/1047

1/837

1/659

1/512

1/393

1/300

1/227

1/171

1/128

1/96

1/72

1/4897

1/4336

1/2869

1/2490

1/2490

1/1755

1/1429

1/1142

1/899

1/698

1/537

1/409

1/310

1/233

1/175

1/131

1/98

1/18013

1/15951

1/10554

1/9160

1/7775

1/6458

1/5256

1/4202

1/3307

1/2569

1/1974

1/1505

1/1139

1/858

1/644

1/481

1/359

Table 3- Risk of trisomy 13 (Snijders et al. Fetal Diag Ther 1995;10:356–67)

Gestational age

10 weeks

12 weeks

14 weeks

16 weeks

20 weeks

40 weeks

20

25

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

1/6347

1/5621

1/3719

1/3228

1/2740

1/2275

1/1852

1/1481

1/1165

1/905

1/696

1/530

1/401

1/302

1/227

1/170

1/127

1/7826

1/6930

1/4585

1/3980

1/3378

1/2806

1/2284

1/1826

1/1437

1/1116

1/858

1/654

1/495

1/373

1/280

1/209

1/156

1/9389

1/8314

1/5501

1/4774

1/4052

1/3366

1/2740

1/2190

1/1724

1/1339

1/1029

1/784

1/594

1/447

1/335

1/251

1/187

1/11042

1/9778

1/6470

1/5615

1/4766

1/3959

1/3222

1/2576

1/2027

1/1575

1/1210

1/922

1/698

1/526

1/395

1/295

1/220

1/14656

1/12978

1/8587

1/7453

1/6326

1/5254

1/4277

1/3419

1/2691

1/2090

1/1606

1/1224

1/927

1/698

1/524

1/392

1/292

1/42423

1/37567

1/24856

1/21573

1/18311

1/15209

1/12380

1/9876

1/7788

1/6050

1/4650

1/3544

1/2683

1/2020

1/1516

1/1134

1/846