INTRODUCTION
Edward's syndrome is the second most common autosomal
trisomy. There is a preponderance of females to males
(3:1) and as with other autosomal trisomies, there
is an association with increased maternal age.
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ANTENATAL
The most common means of prenatal diagnosis is
by routine fetal anomaly ultrasound scan. Trisomy
18 is one of the rare causes of early growth restriction.
Most cases of suspected early growth retardation
are due to inaccurate dating from LMP. In cases of
trisomy 18 the initial ultrasound measurements will
usually be smaller than anticipated, but the initial
action taken will usually be to re-date the pregnancy.
Trisomy 18 should be suspected if fetal measurements
have fallen further behind the anticipated centile
at subsequent scans.
Many women undergo serum screening for trisomy
21 (Down's syndrome) using measurements of alphafetoprotein
(AFP) and human chorionic gonadotrophin (HCG) at
16 to 20 weeks gestation. In trisomy 18 HCG levels
are low, the reason for this is unknown, but it seems
likely that the HCG response in trisomy 18 pregnancies
is poor, perhaps suggesting one mechanism in which
spontaneous miscarriage may be mediated.
Mid-line defects and defects in lateralisation
are common, these include holoprosencephaly and facial
clefts. Characteristic of this syndrome are clenched
hands with the 2nd and 5th fingers overlapping the
3rd and 4th. Flexion deformities may be seen with
talipes, rocker bottom and feet and a prominent heel.
Other ultrasound features associated with trisomy
18 include cystic hygromata and choroid plexus cysts.
Most pregnancies affected by trisomy 18 (approximately
75%) will fail spontaneously. The mechanism for this
in the third trimester is usually placental. If the
presentation of the case is as "placental failure",
there is unlikely to be enough time to consider karyotyping
and many of the cases not diagnosed prenatally will
end with caesarean section delivery.
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POSTNATAL
Most live born infants die within the first week
but occasionally infants survive for several years.
All are affected by severe mental retardation and
poor sucking means many fail to thrive and tube feeding
may be necessary. Other associated anomalies include
cardiac, renal (renal hypoplasia, cystic dysplasia),
and gastrointestinal (atresia, malabsorption and
exomphalos) malformations.
Babies have a characteristic facial appearance including low set ears, micrognathia,
a long cranium with a narrow prominent occiput, microcephaly, and narrow sloping
palpebral fissures.
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WEST MIDLANDS
DATA
Data to follow
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