20.05.13 Summary of ultrasound findings and chromosome abnormalities

Question 1

How many ultrasound scans are offered to women during pregnancy

Answer 1

2

Question 2

What 3 major groups of fetal abnormality are diagnosed by USS

Answer 2

• Neural tube defects
• Chromosome abnormalities
• Congenital heart defects

Question 3

What information is obtained during first trimester ultrasound examination

Answer 3

• Between 11 and 14 weeks
• Check viability of pregnancy
• Pregnancy dating and calculation of estimated date of delivery
• Identifies multiple pregnancies
• Placental localisation
• Detecting fetal anomalies

Question 4

What is nuchal translucency

Answer 4

• Subcutanenous collection of fluid under the skin of the fetal neck.
• Greater or equal to 3.5mm is significant
• Possible causes= cardiac failure due to structural malformation, abnormal lymphatic system
• Associated with increased risk of chromosomal disorders (trisomy 21,18,13 and Turner’s syndrome).

Question 5

What percentage of fetuses with increased nuchal translucency will have an aberrant karyotype

Answer 5

• 75-80%

- E.g. Down syndrome

Question 6

When is nuchal translucency measured

Answer 6

-First trimester combined screening programme.

Question 7

Examples of major structural malformations detected during first trimester

Answer 7

• Holoprosencephaly: failure of brain to divide into lobes and hemispheres
• Omphalocele: herniation of fetal abdominal contents due to failure of abdomen to close around umbilical cord.
• Megacystis: enlarged fetal bladder due to ureteric obstruction
• Limb abnormalities: e.g. shortening of long bones, polydactyly, talipes

Question 8

When is mid-trimester fetal anomaly scan

Answer 8

18 weeks and 20 weeks

Question 9

What ultrasound abnormalities are seen in mid-trimester fetal anomaly scan in trisomy 21 fetuses (Downs syndrome)

Answer 9

• Brachycephaly, nasal hypoplasia, nuchal oedema, cardiac defects (AVSDs), duodenal atresia, echogenic bowel.
• Only 25% second trimester Downs syndrome fetuses have major congenital anomalies detectable by USS.

Question 10

What ultrasound abnormalities are seen in mid-trimester fetal anomaly scan in trisomy 18 fetuses (Edwards syndrome)

Answer 10

-Absent corpus callosum, facial cleft, micrognathia, heart defects, renal defects, echogenic bowel, diaphragmatic hernia, IUGR, decreased placental volume

Question 11

What ultrasound abnormalities are seen in mid-trimester fetal anomaly scan in trisomy 13 fetuses (Patau’s syndrome)

Answer 11

-Holoprosencepahly, cleft lip and palate, IUGR, microcephaly, cardiac and renal (large and echogenic) abnormalities.

Question 12

What is normal variant screening

Answer 12

• Variations in normal fetal anatomy that are unlikely to be clinically significant (apart from relationship to aneuploidy).
• e.g. echogenic foci in heart, two vessel cord, echogenic bowel.
• Generally, if a woman is low risk through screening, not referred for invasive testing if normal variants are observed.
• Exceptions= NT >6mm, echogenic bowel (density equivalent to bone), small measurements (less than 5th centile)