ultrasound diagnosis of fatal anomalies

9 Chromosomal Disorders
General Considerations
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Chromosomal aberrations are the most frequent
and significant disorders and are detected in five
per 1000 live births. The forms vary widely, ranging
from those causing no clinical symptoms (for
example, balanced translocation), to those of
little significance for the affected individual (e.g.,
Klinefelter syndrome), up to those with a fatal
outcome (trisomy 13, 18). As the consequences
for the affected families are serious, diagnosis of
chromosomal anomalies has always been the
main aim of prenatal screening, taking into account
all the ethical considerations involved.
Amniocentesis was developed over 30 years
ago and has been increasingly included in antenatal
care for older pregnant women. In Germany,
this has had legal consequences. In effect,
the gynecologist is obliged to guarantee a chromosomally
healthy child and to document the
fact that adequate patient information regarding
invasive prenatal diagnosis has been provided if
the mother is going to be over the age of 34 at the
expected date of delivery.
In fact, however, only a small percentage of affected
fetuses are detected prenatally on the
basis of the age indication. In order to offer
younger mothers the option of detecting the
most frequent chromosomal anomaly—Down
syndrome—without the risks of amniocentesis,
the triple test was first developed some 10 years
ago. The disadvantage of this test is that, at a cutoff
level of 1 : 350, it has a false-positive rate of
5–10%, with a detection rate of 60–65%.
In recent years, the measurement of nuchal
translucency (NT)at 11–13 weeks has been increasingly
carried out for early detection of
genetic and organ anomalies in younger
mothers. The sensitivity of this method for detecting
Down syndrome, is 70–80%, with a 5%
rate of false-positive findings. In addition to ultrasound
scanning, determination of PAPP-A and
free -HCG raises the sensitivity to 90%. This allows
many pregnant women above the age of 35
years to avoid invasive prenatal diagnosis, which
have their own risks. However, it should be
borne in mind here that a sensitivity of 90%
means that one in 10 affected fetuses will not be
detected.
Self-Help Organizations
Title: The Genetic Alliance
Description: Consortium of support groups
dedicated to helping individuals and families
affected by genetic disorders. Information and
referrals to support groups and genetic services.
Scope: National network
Telephone: 1–800–336–4363 or 202–966–
5557
Fax: 202–966–8553
E-mail: info@geneticalliance.org
Web: http://geneticalliance.org
Title: Chromosome 22 Central
Description: Networking and support for
parents of children with any chromosome disorder.
Supports research. Offers newsletter,
literature, phone support and pen pals.
Scope: International network
Founded: 1996
Address: 2327 Kent Ave., Timmons, Ontario
P4 N 3 C3, Canada
Telephone: 705–268–3099
Fax: 705–268–3099
Web: http://www.c22c.org
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