genifllemifl juguler lenfatiklerle birlikte oldu¤u düflünül-
mektedir. Yayg>n olan teori, lenfanjiyogenezde bir kusur
ve lenfatik gelifliminde gecikme oldu¤udur. Di¤er olas>
etyolojiler, kalp yetmezli¤i ve anormal ekstrasellüler
matrikstir, fakat bunlar NT'nin bölgesel ve geçici olma
özelli¤ini aç>klamaz. En olas> olan, etiyolojinin pek çok
faktörün kompleks etkileflimi olmas>d>r.
10
NT, normal
olarak, ilerleyen gebelik haftas> ile artar, bu nedenle öl-
çümün bafl-popo mesafesi ("crown-rump length,
CRL") ile k>yaslanmas> gerekir. Ço¤u normal fetüste in-
ce bir NT görülür. CRL'ye göre 95 persantilin üzerinde-
ki bir NT kal>n kabul edilir. 99 persantilden fazla bir
NT ise, CRL ile anlaml> de¤iflim göstermez ve yaklafl>k
3.5 mm'dir.
11
1121
B
ÖLÜM
31
Kromozom Anomalileri
TABLO 31-1. ANNE YAfiI VE GESTASYONA GÖRE TR
TAHM
Gestasyon Yafl> (hafta)
ANNE
YAfiI (YIL)
10
12
14
16
20
40
Trizomi 21
20
1/983
1/1068
1/1140
1/1200
1/1295
1/1527
25
1/870
1/946
1/1009
1/1062
1/1147
1/1352
30
1/576
1/626
1/668
1/703
1/759
1/895
31
1/500
1/543
1/580
1/610
1/658
1/776
32
1/424
1/461
1/492
1/518
1/559
1/659
33
1/352
1/383
1/409
1/430
1/464
1/547
34
1/287
1/312
1/333
1/350
1/378
1/446
35
1/229
1/249
1/266
1/280
1/302
1/356
36
1/180
1/196
1/209
1/220
1/238
1/280
37
1/140
1/152
1/163
1/171
1/185
1/218
38
1/108
1/117
1/125
1/131
1/142
1/167
39
1/82
1/89
1/95
1/100
1/108
1/128
40
1/62
1/68
1/72
1/76
1/82
1/97
41
1/47
1/51
1/54
1/57
1/62
1/73
42
1/35
1/38
1/43
1/43
1/46
1/55
43
1/26
1/29
1/30
1/32
1/35
1/41
44
1/20
1/21
1/23
1/24
1/26
1/30
45
1/15
1/16
1/17
1/18
1/19
1/23
Trizomi 18
20
1/1993
1/2484
1/3015
1/3590
1/4897
1/18013
25
1/1765
1/2200
1/2670
1/3179
1/4336
1/15951
30
1/1168
1/1456
1/1766
1/2103
1/2869
1/10554
31
1/1014
1/1263
1/1533
1/1825
1/2490
1/9160
32
1/860
1/1072
1/1301
1/1549
1/2490
1/7775
33
1/715
1/891
1/1081
1/1287
1/1755
1/6458
34
1/582
1/725
1/880
1/1047
1/1429
1/5256
35
1/465
1/580
1/703
1/837
1/1142
1/4202
36
1/366
1/456
1/553
1/659
1/899
1/3307
37
1/284
1/354
1/430
1/512
1/698
1/2569
38
1/218
1/272
1/330
1/393
1/537
1/1974
39
1/167
1/208
1/252
1/300
1/409
1/1505
40
1/126
1/157
1/191
1/227
1/310
1/1139
41
1/95
1/118
1/144
1/171
1/233
1/858
42
1/71
1/89
1/108
1/128
1/175
1/644
43
1/53
1/66
1/81
1/96
1/131
1/481
44
1/40
1/50
1/60
1/72
1/98
1/359
Trizomi 13
20
1/6347
1/7826
1/9389
1/11042
1/14656
1/42423
25
1/5621
1/6930
1/8314
1/9778
1/12978
1/37567
30
1/3719
1/4585
1/5501
1/6470
1/8587
1/24856
31
1/3228
1/3980
1/4774
1/5615
1/7453
1/21573
32
1/2740
1/3378
1/4052
1/4766
1/6326
1/18311
33
1/2274
1/2806
1/3366
1/3959
1/5254
1/15209
34
1/1852
1/2284
1/2740
1/3222
1/4277
1/12380
35
1/1481
1/1826
1/2190
1/2576
1/3419
1/9876
36
1/1165
1/1437
1/1724
1/2027
1/2691
1/7788
37
1/905
1/1116
1/1339
1/1575
1/2090
1/6050
38
1/696
1/858
1/1029
1/1210
1/1606
1/4650
39
1/530
1/654
1/784
1/922
1/1224
1/3544
40
1/401
1/495
1/594
1/698
1/927
1/2683
41
1/302
1/373
1/447
1/526
1/698
1/2020
42
1/227
1/280
1/335
1/395
1/524
1/1516
43
1/170
1/209
1/251
1/295
1/392
1/1134
44
1/127
1/156
1/187
1/220
1/292
1/846
Snijders RJM, Sebire NJ, Nicolaides KH: Maternal age and gestational age-specific risk for chromosomal defects. Fetal Diagn Ther 1995;100:356-367'den al>nm>flt>r.