The 11-14 weeks scan - KH Nicolaides, NJ Sebire, RJM Snijders, AP Souka
 

Chapter 3

TYPES OF ABNORMALITIES ASSOCIATED WITH INCREASED NUCHAL TRANSLUCENCY

A wide range of fetal abnormalities have been reported in fetuses with increased NT and these are summarized in Table 2.

The observed prevalence for some of the abnormalities, such as anencephaly, holoprosencephaly, gastroschisis, renal abnormalities and spina bifida, may not be different from that in the general population.

However, the prevalence of major cardiac defects, diaphragmatic hernia, exomphalos, body stalk anomaly, skeletal defects, and certain genetic syndromes, such as congenital adrenal hyperplasia, fetal akinesia deformation sequence, Noonan syndrome, Smith-Lemli-Opitz syndrome and spinal muscular atrophy, appears to be substantially higher than in the general population and it is therefore likely that there is a true association between these abnormalities and increased NT.


Table 2. Fetal abnormalities reported in fetuses with increased nuchal translucency thickness.

ABNORMALITY    
Central nervous system defect Gastrointestinal defect Fetal anemia
Acrania / anencephaly Crohn's disease Blackfan Diamond anaemia
Agenesis of the corpus callosum Duodenal atresia Congenital erythropoietic porphyria
Craniosynostosis Esophageal atresia Dyserythropoietic anaemia
Dandy Walker malformation Small bowel obstruction Fanconi anemia
Diastematomyelia   Parvovirus B19 infection
Encephalocele Genitourinary defect Thalassaemia-α (*)
Fowler syndrome Ambiguous genitalia  
Holoprosencephaly Congenital adrenal hyperplasia Neuromuscular defect
Hydrolethalus syndrome Congenital nephrotic syndrome Fetal akinesia deformation sequence
Iniencephaly Hydronephrosis Myotonic dystrophy (*)
Joubert syndrome Hypospadias Spinal muscular atrophy (*)
Macrocephaly Infantile polycystic kidneys  
Microcephaly Meckel-Gruber syndrome Metabolic defect
Spina bifida Megacystis Beckwith-Wiedemann syndrome
Trigonocephaly C Multicystic dysplastic kidneys GM1 gangliosidosis (*)
Ventriculomegaly Renal agenesis Long-chain 3-hydroxyacyl-coenzyme A Dehydrogenase deficiency (*)
    Mucopolysaccharidosis type VII (*)
Facial defect Skeletal defect Smith-Lemli-Opitz syndrome (*)
Agnathia/micrognathia Achondrogenesis Vitamin D resistant rickets
Facial cleft Achondroplasia Zellweger syndrome (*)
Microphthalmia Asphyxiating thoracic dystrophy  
Treacher-Collins syndrome Blomstrand osteochondrodysplasia Other defect
  Campomelic dwarfism Body stalk anomaly
Nuchal defect Cleidocranial dysplasia Brachmann-de Lange syndrome
Cystic hygroma Hypochondroplasia Charge association
Neck lipoma Hypophosphatasia Deficiency of the immune system
  Jarcho-Levin syndrome Congenital lymphedema
Cardiac defect Kyphoscoliosis EEC syndrome
Di George syndrome Limb reduction defect Neonatal myoclonic encephalopathy
  Nance-Sweeney syndrome Noonan syndrome
Pulmonary defect Osteogenesis imperfecta Perlman syndrome
Cystic adenomatoid malformation Roberts syndrome Stickler syndrome
Diaphragmatic hernia Robinow syndrome Unspecified syndrome
Fryn syndrome Short-rib polydactyly syndrome Severe developmental delay
  Sirenomelia  
Abdominal wall defect Talipes equinovarus  
Cloacal exstrophy Thanatophoric dwarfism  
Exomphalos VACTER association  
Gastroschisis    
 
Cardiac defects

There is a high association between increased NT and cardiac defects in both chromosomally abnormal and normal fetuses (Hyett et al 1977, 1999). Eight studies have reported on the screening performance of NT thickness for the detection of cardiac defects (Souka et al 2004). In total, 67,256 pregnancies were examined and the prevalence of major cardiac defects was 2.4 per 1,000. For a false positive rate of 4.9%, the detection rate of cardiac defects was 37.5%. A meta-analysis of screening studies reported that the detection rates were about 37% and 31% for the respective NT cut-offs of the 95th and 99th centiles (Makrydimas et al 2003). In chromosomally normal fetuses, the prevalence of major cardiac defects increases exponentially with NT thickness from 1.6 per 1,000 in those with NT below the 95th centile, to about 1% for NT of 2.5-3.4 mm, 3% for NT of 3.5-4.5 mm, 7% for NT of 4.5-5.4 mm, 20% for NT of 5.4-6.4 mm and 30% for NT of 6.5 mm or more (Souka et al 2004).

The clinical implication of these findings is that increased NT constitutes an indication for specialist fetal echocardiography. Certainly, the overall prevalence of major cardiac defects in such a group of fetuses (1-2%) is similar to that found in pregnancies affected by maternal diabetes mellitus or with a history of a previously affected offspring, which are well accepted indications for fetal echocardiography. At present, there may not be sufficient facilities for specialist fetal echocardiography to accommodate the potential increase in demand if the 95th centile of nuchal translucency thickness is used as the cut-off for referral. In contrast, a cut-off of the 99th centile would result in only a small increase in workload and, in this population the prevalence of major cardiac defects would be very high.

Patients identified by NT scanning as being at high risk for cardiac defects need not wait until 20 weeks for specialist echocardiography. Improvements in the resolution of ultrasound machines have now made it possible to undertake detailed cardiac scanning in the first trimester of pregnancy. A specialist scan from 13 weeks can effectively reassure the majority of parents that there is no major cardiac defect. In the cases with a major defect, the early scan can either lead to the correct diagnosis or at least raise suspicions so that follow-up scans are carried out.

The finding that increased NT is not confined to specific types of cardiac defects has potentially important implications in terms of developing strategies of screening for major cardiac defects. Major defects, such as tetralogy of Fallot, transposition of the great arteries and coarctation of the aorta are rarely detected by routine second-trimester examination of the four-chamber view. However, a high proportion of these abnormalities present with increased NT. Consequently, increased NT and abnormal four-chamber view may constitute complementary indications for specialist fetal echocardiography resulting in a substantially improved prenatal detection of congenital cardiac defects.


Body stalk anomaly

This lethal, sporadic abnormality is found in about 1 in 10,000 fetuses at 10-13+6 weeks. The ultrasonographic features are major abdominal wall defect, severe kyphoscoliosis and short umbilical cord with a single artery (Daskalakis et al). The upper half of the fetal body is seen in the amniotic cavity, whereas the lower part is in the celomic cavity, suggesting that early amnion rupture before obliteration of the celomic cavity is a possible cause of the syndrome. Although the fetal NT is increased in about 85% of the cases, the karyotype is usually normal.


Diaphragmatic hernia

Increased NT thickness is present in about 40% of fetuses with diaphragmatic hernia, including more than 80% of those that result in neonatal death due to pulmonary hypoplasia and in about 20% of the survivors (Sebire et al 1997). It is possible that in fetuses with diaphragmatic hernia and increased NT the intrathoracic herniation of the abdominal viscera occurs in the first trimester and prolonged compression of the lungs causes pulmonary hypoplasia. In the cases where diaphragmatic hernia is associated with a good prognosis, the intrathoracic herniation of viscera may be delayed until the second or third trimesters of pregnancy.


Exomphalos

At 11-13+6 weeks the incidence of exomphalos is about 1 in 1,000 and the incidence of chromosomal defects, mainly trisomy 18, is about 60% (Snijders et al 1995). Increased NT is observed in about 85% of chromosomally abnormal and 40% of chromosomally normal fetuses with exomphalos.


Megacystis

Fetal megacystis at 11-13+6 weeks of gestation, defined by a longitudinal bladder diameter of 7 mm or more, is found in about 1 in 1,500 pregnancies. Megacystis is associated with increased NT, which is observed in about 75% of those with chromosomal abnormalities, mainly trisomy 13, and in about 30% of those with normal karyotype (Liao et al 2003).


Genetic syndromes

The genetic syndromes associated with increased NT are summarised in Table 3.


Table 3. Genetic syndromes reported in fetuses with increased nuchal translucency thickness

Genetic syndrome

Inheritance

Birth prevalence

Prognosis and common sonographically detectable abnormalities

Achondrogenesis

AR

1 in 40,000

Lethal skeletal dysplasia. Severe limb shortening, narrow thorax, hypomineralization of the vertebral bodies. Mineralisation of the skull normal in type II and poor in type I.

Achondroplasia*

AD

1 in 26,000

Intelligence and life expectancy are normal. Short limbs, macrocephaly, depressed nasal bridge, lumbar lordosis and short limbs, usually after 22 weeks

Adrenal hyperplasia*

AR

1 in 5,000

Deficiency in one of the enzymes of cortisol biosynthesis, resulting in overproduction of cortisol precursors and androgens. Increased NT, ambiquous genitalia in females.

Asphyxiating thoracic dystrophy

AR

1 in 70,000

Variable prognosis from neonatal death to normal survival. Narrow chest and rhizomelic limb shortening, which may not become apparent until after 22 weeks.

Beckwith–Wiedemann syndrome

Sporadic

1 in 14,000

In some cases, there is mental handicap, which is thought to be secondary to inadequately treated hypoglycemia. About 5% develop tumors during childhood, most commonly nephroblastoma and hepatoblastoma. Prenatal sonographic features include macrosomia and exomphalos.

Blackfan-Diamond anemia

AD, AR

1 in 200,000

Congenital hypoplastic anemia requiring treatment with steroids and repeated blood transfusions. The risk of hematologic malignancies, mainly acute leukemia, is increased. Thumb defects, hypertelorism, cardiac and urogenital anomalies.

Blomstrand osteochondrodysplasia

AR

Rare

Lethal skeletal dysplasia. Severe limb shortening, narrow thorax, increased bone density.

Brachmann-Cornelia de Lange syndrome

AD

1 in 160,000

Mental handicap. Fetal growth restriction, short limbs, heart defects, diaphragmatic hernia.

Campomelic dysplasia

AR

1 in 200,000

Lethal skeletal dysplasia. Short and bowed lower limbs with narrow thorax.

CHARGE association

Sporadic

Rare

Acronym for Coloboma of the eye, Heart anomaly, choanal Atresia, growth and mental Retardation, Gonadal hypoplasia and Ear abnormalities and/or deafness. There may not be any antenatal sonographic findings.

Cleidocranial dysplasia

AD

Rare

Normal life expectancy. Hypoplastic clavicles and nasal bone.

Di George syndrome

Sporadic

1 in 4,000

Results from de novo 22q11 deletion in 90% of cases. Characterized by neonatal hypocalcemia, due to hypoplasia of the parathyroid glands, and susceptibility to infection due to hypoplasia or aplasia of the thymus gland. A variety of cardiac malformations are seen, including tetralogy of Fallot, interrupted aortic arch, truncus arteriosus, right aortic arch and aberrant right subclavian artery. Short stature and mild to moderate learning difficulties are common.

Dyserythropoietic anemia

AD, AR

Rare

Congenital, usually mild anemia. In some cases there is severe anemia presenting with fetal hydrops.

Ectrodactyly-ectodermal dysplasia-cleft palate syndrome

AD

Rare

Wide variability in phenotypic expression. Split hand and foot, cleft lip and/or palate.

Erythropoietic porphyria (Gunther’s disease)

AR

Rare

Usually presents during childhood with severe cutaneous photosensitivity with progressive bullous lesions, leading to infection, bone resorption, cutaneous deformity and chronic hemolytic anemia. Severe cases present with fetal hydrops.

Fanconi anemia

AR

1 in 22,000

Congenital aplastic anemia characterised by pancytopenia and spontaneous chromosome instability. The phenotype and age of onset are variable. There may be no prenatal sonographically detectable abnormalities.

Fetal akinesia deformation sequence

AR, sporadic

Rare

Heterogeneous group of conditions resulting in multiple joint contractures, frequently associated with fetal myopathy, neuropathy or an underlying connective tissue abnormality. Severe cases present with arthrogryposis and increased NT in the first trimester.

Fowler syndrome

AR

Rare

Proliferative vasculopathy of the central nervous system that leads to disruption, disorganisation and hemorrhagic necrosis of the developing brain. Prenatal features include hydranencephaly and arthrogryposis.

Fryn syndrome

AR

1 in 15,000

Usually lethal. Diaphragmatic hernia, digital defects, short webbed neck.

GM1-Gangliosidosis*

AR

Rare

Progressive neurological deterioration, resulting in early and severe retardation of both motor and mental development. Death occurs within the first 10 years of life from chest infections. Prenatal sonographic findings include visceromegaly and generalized edema.

Hydrolethalus syndrome

AR

1 in 20,000

Lethal condition characterized by hydrocephalus, absent corpus callosum, facial cleft, micrognathia, polydactyly, talipes and cardiac septal defects.

Hypochondroplasia

AD

1 in 26,000

Resembles achondroplasia and is characterised by short-limb dwarfism manifesting during childhood. Prenatally there may be short limbs and macrocephaly.

Hypophosphatasia

AR

1 in 100,000

Subdivided into perinatal, infantile, childhood and adult forms, according to the age of onset of symptoms. In the perinatal type there is hypomineralization of the skull and spine, short limbs and narrow thorax.

Infantile polycystic kidney disease

AR

1 in 10,000

Subdivided into perinatal, neonatal, infantile, and juvenile, depending on the severity of the disease and age of presentation. Prenatal sonographic features include large, echogenic kidneys and oligohydramnios.

Jarcho–Levin syndrome

AR

1 in 500,000

Heterogeneous disorder characterized by scoliosis and disorganization of the spine. There are two types. In spondylothoracic dysplasia there is a narrow thorax and lethal respiratory insufficiency in infancy. Spondylocostal dysplasia is associated with survival to adult life but with some degree of physical disability.

Joubert syndrome

AR

Rare

Profound mental retardation and developmental delay. Death usually occurs in the first 5 years of life. Partial or complete absence of the cerebellar vermis

Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency*

AR

Rare

Lethal disorder. Muscular hypotonia, cardiomyopathy, hydrops

Lymphedema

AD

Rare

Hypoplastic/aplastic lymphatic vessels, usually affecting the lower limbs. Three clinical subtypes, congenital (Milroy disease, present at birth), praecox (pubertal onset) and tarda (midlife onset), with congenital lymphedema being the rarest and most severe of the three. There may be no prenatal sonographic findings.

Meckel–Gruber syndrome

AR

1 in 10,000

Lethal. Typical features are encephalocele, bilateral polycystic kidneys, polydactyly.

Mucopolysaccharidosis type VII*

AR

Rare

Mental retardation, short stature, macrocephaly, hearing loss, corneal opacities and recurrent lower respiratory tract infection.

Myotonic dystrophy*

AD

1 in 25,000

The genetic defect is an amplified trinucleotide repeat in a protein kinase gene on chromosome 19. Age of onset and severity of disease vary with the number of repeats. The mutation can worsen progressively in successive generations and the severe congenital form occurs almost exclusively in the offspring of affected women. Prenatal sonographic signs may be decreased fetal movements and polyhydramnios in the third trimester.

Nance–Sweeney syndrome

AR

Rare

Intelligence and life expectancy are normal. Short limbs, vertebral abnormalities.

Nephritic syndrome*

AR

1 in 8,000 in Finland

Renal failure requiring transplantation within the first 4 years of life. Prenatally may present with transient hydrops

Noonan syndrome

AD

1 in 2,000

Life expectancy is probably normal in those without severe heart disease. Mild mental retardation is present in about one-third of cases .

 

 

 

The majority of cases are diagnosed Postnatally. Prenatal sonographic findings include skin edema, hydrothorax, polyhydramnios, and cardiac defects, such as pulmonic stenosis and hypertrophic cardiomyopathy but these may become apparent only in the third trimester.

Osteogenesis imperfecta type II*

AR

1 in 60,000

Lethal skeletal dysplasia. Short limbs and ribs with multiple fractures, hypomineralization of the skull.

Perlman syndrome

AR

Rare

Similar to Beckwith–Wiedemann syndrome. Fetal and neonatal mortality is more than 60% and, in survivors, there is a high incidence of neurodevelopmental delay. Sonographic features include progressive macrosomia and enlarged kidneys.

Roberts syndrome

AR

Rare

Associated with the cytogenetic finding of premature centromere separation and puffing. Characterized by symmetrical limb defects of variable severity (tetraphocomelia), facial cleft, microcephaly and growth restriction.

Robinow syndrome

AR

Rare

Skeletal defect with short forearms, frontal bossing, hypertelorism, and vertebral anomalies

Short-rib polydactyly syndrome

AR

Rare

Lethal skeletal dysplasia. There are four types. Type I (Saldino–Noonan) has narrow metaphyses; type II (Majewski) has facial cleft and disproportionally shortened tibiae; type III (Naumoff) has wide metaphyses with spurs; type IV (Beemer–Langer) is characterized by median cleft lip, extremely short ribs and pro-tuberant abdomen with umbilical hernia. Prenatal sonographic findings include short limbs, narrow thorax and polydactyly

Smith–Lemli–Opitz syndrome*

AR

1 in 20,000

High perinatal and infant mortality and severe mental retardation Prenatal sonographic features include polydactyly, cardiac defects, ambiguous or female external genitalia in the male.

Spinal muscular atrophy type 1*

AR

1 in 7,000

Progressive muscle weakness leading to death before two years of age because of respiratory failure. Decreased fetal movements are commonly reported and symptoms usually start at birth or up to six months of age.

Stickler syndrome

AD

1 in 10,000

Progressive myopia beginning in the first decade of life, resulting in retinal detachment and blindness, sensorineural hearing loss, marfanoid habitus with normal height, premature degenerative changes in various joints. There may be no prenatal sonographic findings but in some cases there is a facial cleft, or micrognathia.

Thalassaemia-α*

AR

Common in Mediterranean and Asian populations

The alpha locus determines a polypeptide chain, the α-chain, which is present in adult hemoglobin (α2/ß2), fetal hemoglobin (α2/α2) and embryonic hemoglobin (α2/α2). Normally there are four alpha gene copies. Absence of all four α-genes results in homozygous α-thalassemia, which presents with hydrops fetalis, usually in the second trimester.

Thanatophoric dysplasia*

Sporadic

1 in 10,000

Lethal skeletal dysplasia. Severe limb shortening, narrow thorax, enlarged head with prominent forehead.

Treacher Collins syndrome

AD

1 in 50,000

Normal life expectancy. Micrognathia, deformities of the ears

Trigonocephaly ‘C’ syndrome

AR

1 in 15,000

About half of the affected individuals die in infancy while survivors are severely mentally handicapped with progressive microcephaly.Trigonocephaly, short nose, prominent maxilla

VACTER association

Sporadic, AR

1 in 6,000

Acronym for Vertebral abnormalities, Anal atresia, Cardiac defects, Tracheo-Esophageal fistula with esophageal atresia, Radial and Renal defects. Prognosis depends on the particular combination and severity of the abnormalities present. Mental function is usually normal.

Vitamin D resistent rickets

AR

Rare

None

Zellweger syndrome*

AR

1 in 25,000

Death occurs in the first two years of life, most commonly due to chest infections and liver failure. Prenatal features include hypertelorism, brain and cardiac defects, hepatomegaly, growth restriction

* Genetic syndromes which are amenable to prenatal diagnosis by DNA analysis

 
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