Objective To evaluate screening for chromosomal defects by a combination of fetal nuchal translucency thickness and maternal age.Design A prospective multicentre screening study where fetal nuchal translucency thickness was measured at 10 to 14 weeks of gestation.
Main outcome measuresTrisomy 21 and other chromosomal defects identified by increased nuchal translucency thickness and by a combination of nuchal translucency thickness and maternal age.
ResultsIn normal fetuses nuchal translucency thickness increased significantly with crown-rump length. The nuchal translucency was above the 95th centile in 77% (66 of 86) of fetuses with trisomy 21 and in 78 YO (61 of 78) of those with other chromosomal defects. On the basis of the distribution of nuchal translucency measurements in normal fetuses and those with trisomy 21, a new method of screening is proposed which involves assessment of individual risk based on the combination of fetal nuchal translucency, crown-rump length and maternal age. The minimum risk was 1/100 in 4.9% of the normal pregnancies, in 80 % of those with trisomy 21 and in 77 % of those with other chromosomal defects.
In an ongoing study involving seven hospitals in London and surrounding areas, 55,237 fetuses were examined by ultrasound at 10-14 weeks of gestation. There were 47 fetuses (1 in 1175) with anencephaly which presented with acrania with varying degrees of cerebral degeneration. The first audit of results was performed in April 1995. During the first phase of the study 34,830 fetuses were examined and in eight of the 31 with anencephaly the diagnosis was not made at the 10-14-week scan. Following the audit, 20,407 fetuses were examined and in all 16 with anencephaly the diagnosis was made at the 10-14-week scan (p = 0.03). These findings demonstrate that anencephaly can be reliably diagnosed at the routine 10-14-week ultrasound scan, provided a specific search is made for the sonographic features for this condition.
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