Ultrasonographers may become deskilled at
measuring nuchal thickness
ultrasound departments to accommodate the increasing number of third trimester scans which are being requested following the RCOG guidance surrounding detection of small for gestational age fetuses13
.
Disadvantages to stopping serum screening HCG and PAPP-A are potentially useful for screening for other conditions, for example in predicting pre-eclampsia or intrauterine growth restriction1
. Alpha fetoprotein is used to screen for open neural defects in the fetus4 . If these are
removed from the screening program for Down’s syndrome, fetuses at risk of these conditions may go undetected. The ffDNA test identifies only trisomies 21, 18 and 13 and not the full karyotype. This means invasive testing would still be needed if an increased nuchal or other structural anomalies were detected, so that other chromosomal causes could be excluded3
.
Future applications Testing for trisomy 18 and 13 is now also available via ffDNA in the USA, Germany, Hong Kong and China. It is also available privately in the UK3
close to 100% and sensitivities and specificities close to 100%1,6 sensitivities and specificities closer to 90%1,3 chromosome linked conditions in some countries.
. Screening for gender with ffDNA is also used for those at risk of sex
Ethical challenges As a straight forward procedure, free of physical danger, there is a concern that ffDNA testing may be taken for granted as a ‘routine’ blood test. As a result, the importance of thorough counselling into the conditions the test may detect could be forgotten. Informed consent is a vital part of involving parents in the decision making process. Sayres et al found that whilst 47% of individuals were interested in ffDNA testing, 29% of couples were not interested in any form of screening10
. Testing these individuals without thorough counselling compromises their autonomy and leaves them with
knowledge they would rather not have. As it is now possible to screen for more and more genetic conditions using ffDNA, the ethics involved become even
more important. It is possible to screen for conditions such as Huntingdon’s disease, but should we be screening in utero for conditions that may not affect the fetus until it reaches adulthood? If and when the technology advances, should ffDNA be used to look at the whole fetal karyotype, or just specific conditions such as Down’s syndrome? The authors believe ffDNA should, and will, be implemented into the NHS screening program in the medium term
as a first line screening tool. However, this cannot occur without careful planning into the consequences of changing established practice, and ensuring that the laboratory capacity is available to meet demand.
-24-
. For trisomy 18 the false positive rate is quoted as 0.2% with a negative predictive value . The test for trisomy 13 is not quite as accurate with
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68