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Ultrasound Screening
Main and Danish guidelines by the web master
Major anomalies and Aneuploid Risk Seen on Ultrasound
B : birth LB : livebirth IA : infant autopsy If both parents have normal blood chromosomes, trisomy 21 is usually presumed to have arisen (de novo), and the observed recurrent risk in a series of trisomic cases was less than 1%. Gonadal mosaicism for isochromosome 21 has been reported and recurrences of Down Syndrome are recorded, a rounded-up 1% risk of recurrence is appropriate. When one parent is shown to carry a balanced robertsonian translocation that has given rise to a child affected by Down Syndrome, the risk of recurrence mainly depends on the sex of the carrier parent: if the mother is a carrier, the risk of recurrence at amniocentesis is 15% (closer to 10% at term due to fetal demise after 16 weeks' gestation), compared with a much lower risk of less than 5%, even less than 1%, if the father is the translocation carrier. Down Syndrome. The additional type of chromosome 21 usually results from nondisjunction (failure to separate during meiosis I or meiosis II). The errors are almost all of maternal origin, only 5% occurs during spermatogenesis. In 5% the extra chromosome 21 appears to be due to an error in mitosis and not associated with increased maternal age. Translocation trisomy 21 with a majority of new mutations are nearly always of maternal origin. 3-4% of cases of Down due to unbalanced translocation are born to a parent with a balance Robertson translocation. Down Syndrome recurrence risks. The risk of the recurrence trisomy 21 in children of mothers who had one liveborn affected infant: when the mother was age under 30, the recurrence risk is 1.4%, and this figure is clearly increased above the background rate of about 0.7%. But when the mother was older, the trisomy 21 recurrence risk is not clearly increased above the background maternal age risk. Parent with Trisomy 21 Rarely women wiwth trisomy 21 become pregnant, and in this situation the risk of trisomy 21 in the offsprting is close to 50%. Fertillity in males with trisomy 21 is exceptional, but there are at least two well-documented reports of an affected male fathering an unaffected child. Soft ultrasound markers in trisomy The absence of any markers conveys a 70% reduction in Down Syndrome prior risk. Nasal hypoplasia Nasal hypoplasia at 15-24 weeks of gestation has been reported as a strong marker for trisomy 21. Nasal hypoplasia is present in 60-65% of the trisomy 21 fetuses defined as a nasal bone that is not visible or with a length of <2.5 mm. Nasal bone is absent in 1,4% of the population and the reported likelihood ratio for trisomy 21 is 146 (50- to 434) for absence of the nose bone and 0.27 (0.18 to 0.40) for present of nose bone. Absence of nose bone is seen in up to 10% in African Carribbeans. Combining nuchal translucency and age in trisomy 21 with the use of presence or absence of the nose bone increase the sensitivity to 85% and decrease of the false- positive rate to about 1%. Absent nose bone has also been described in fetuses with fragile X. Soft ultrasound markers in trisomy The absence of any markers conveys a 70% reduction in Down Syndrome prior risk. Prevalence of major and minor defects or markers in the second trimester scan in trisomy 21 and chromosomally normal fetuses in the combined data of two major series (Nyberg et al 2001; Bromley et al 2002). From these data the positive and negative likelihood ratios (with 95% confidence interval) for each marker can be calculated in the last column is the likelihood ratio for each marker found in isolation.
From the 11-14 weeks scan. K.H. Nicolaides 2004. 
Choroid plexus cystfound in 1-2% (3-6 mm) and 95% resolves after 26 weeks. Seen in 25-30% of fetus with trisomy 18, but the vast majority will have other abnormalities. A recent study found 0.5% with aneuploidy with a risk 0.36 (0.4 to 1.3) < 36 years and 2.4 (0.06 to 12.6) > 36 years. Most do not support karyotyping as an isolated finding as the overall risk is marginal increased. If one additional If abnormality is found maternal age risk increases about 20 folds.
Echogenic bowel is 0.5-1% has echogenicity of the fetal small bowel similar or greater than that of the surrounding bone. Also seen in meconium ileus secondary to cystic fibrosis, congenital infection, intra-amniotic bleeding and severe IUGR. The most prevalent chromosome abnormality is trisomy 21. The risk is 3-5 times the background risk adjusted to maternal age.
Mild hydronephrosis (3-4 to 10 mm), trisomy 21 increased risk by factor 1.6 but some don't find any increase risk as an isolated finding.
Short proximal bones: Trisomies 21, 18, triploidy and Turner syndrome are associated with relative shortening of the long bones. Syndactyly is accociated with triploidy, clinodactyly and sandal gap with trisomy 21 (up to 45%), polydactyly with trisomy 13, overlapping fingers, rocker bottom feet and talipes with trisomy 18.
Ventriculomegaly: (1:1000) 10-12 mm (15 mm) mild or borderline ventriculomegaly caused later severe brain abnormality in 5%, 15% mild problems later. The commonest chromosomal defects are trisomies 21, 18, 13 and triploidy. The prevalence of chromosomal defects is higher in those with mild to moderate, rather than severe ventriculomegaly. The risk in case of no other abnormalities is low.
Holoprosecencephaly: 1 per 10,000. The prevalence of chromosomal defects is about 30% and the commonest are trisomies 13 and 18. Chromosomal defects are only increased in fetuses with holoprosencephaly and extrafacial defects.
Dandy-Walker Malformation: (1:3000) Complete or partial agenesis of the cerebellar vermis and enlarged posterior fossa. The variant (partial agenesis of the cerebellar vermis without enlargement of the posterior fossa and mega-cisterna magna) is found in 4-12% of all cases of infantile hydrocephalus. 1 per 30,000. Chromosomal defects is about 40% usually trisomies 18 or 13 and triploidy.
Facial cleft. 1 per 800 live births. Chromosomal defects are found in less than 1% of babies with facial cleft. However, in prenatal series the prevalence is about 40%, most commonly trisomies 13 and 18 as the patients are pre-selected and include many fetuses with multiple other defects.
Cardiac abnormalities: Abnormalities of the heart and great arteries are found in 4-7 per 1,000 live births and in about 30 per 1,000 stillbirths. Chromosomal defect is seen in 25% of cases. The most common defects are trisomies 21, 18, 13 and Turner syndrome.
Exomphalos: 1 in 4,000. Chromosomal defects, mainly trisomies 18 and 13, are found in about 30% at mid-gestation and in 15% of neonates. The prevalence of chromosomal abnormalities is four times higher when the exomphalos sac contains only bowel than in cases where only the liver is included.
Exophageal atresia. 1 in 30,000. Chromosomal defects are found in 3-4% of affected neonates, mainly trisomy 18.
Duodenal atresia. 1 in 5,000. Trisomy 21 is found in about 40% of cases. Autosomal recessive pattern of inheritance is seen.
Urinary tract abnormalities. The prevalence of chromosomal in females is double than in males. In mild hydronephrosis, the commonest chromosomal defect is trisomy 21, whereas in moderate/severe hydronephrosis, multicystic kidneys, or renal agenesis the commonest defects are trisomies 18 and 13.
Other markers are iliac angle >90%, sensitivity 95%, false positive rate 25% in Trisomy 21
Increased nuchal translucencywith a normal karyotype
Prevalence of major cardiac defects in fetuses with increased nuchal translucency thickness at 11 to 13+6 weeks.
Skeletal defects and certain genetic syndromes such as congenital adrenal hyperplasia, fetal akinesia deformation sequence, Noonan syndrome, Smith-Lemli-Opizz syndrome and spinal muscular atrophy, appears to be substantially higher than in the general population. Relation between nuchal translucency thickness and prevalence of chromosomal defects. , miscarriage or fetal death and major fetal abnormalities of the last column is the estimated prevalence of delivery of a healthy baby with no major abnormalities. Relation between nuchal translucency thickness and prevalence of chromosomal defects. , miscarriage or fetal death and major fetal abnormalities of the last column is the estimated prevalence of delivery of a healthy baby with no major abnormalities.
(1) Cicero S, et al. Absence of nasal bone in fetuses with trisomy 21 at 11-14 weeks of gestation: an observational study. The Lancet 2001;358:1665-1667. (2) Nicolaides Kypros H. The 1-13 weeks scan. (3) Nyberg DA, Soubi VL: Sonographic markers of fetal trisomies. Ultrasound Med 20;665:2001 (4) Twining P, McHugo JM, Pilling DW. Textbook of Fetal Abnormalities. Churchill Livingstone. Harcourt Publishers Limited 2000. (5) Rimoin PC et al. Down Syndrome Recurrence Risks. Principles and Practice of Medical Genetic 2006
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