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CAR: Anomalies - Chromosome
Edwards Syndrome

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Introduction Antenatal Postnatal West Midlands Data


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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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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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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Data to follow

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© Perinatal Institute 2011