Down syndrome Counselling

Question 1

A 38-year-old G2P1 is concerned about having a child with Down syndrome. What tests are available and how would you counsel the patient regarding the possible results?

Answer 1

Impression
Key feature is the patient’s concern about having a child with Down syndrome. Priorities in this consult would be

1 - Taking thorough Hx/Ex/Ix to guide interpretation
2 - Patient education about risks of DS child
3 - Counselling re tests available and what results will mean

Question 2

Down syndrome counselling - History

Answer 2

History:
Focus on risk factors and patient understanding of trisomy.
- sx: symptoms of current pregnancy, details of conception (IVF,
- RISK: advanced maternal age, previous T21 birth,
- assess understanding of T21
- Antenatal history
- obstetric history
- SNAP

Question 3

Down syndrome counselling - Examination

Answer 3

Examination

• general appearance + vitals
• antenatal assessment: fundal height, BP, fetal doppler, abdominal palpation

Question 4

Down syndrome counselling - Screening options

Answer 4

Screening options
1 - combined first trimester screening (11-13 wks)
- combines PAPP-A, nuchal translucency, maternal age, ß-HCG to calculate risk of DS
- involves both a blood test and an abdominal ultrasound at 11-13 wks gestation
- reported as high-risk (>1/300) or low (<1/300)

2 - Non-invasive prenatal screening test (NIPT)

• is a maternal blood test looking for cell-free fetal DNA in maternal circulation, conducted at 10+ weeks gestation
• detects 3 chromosomal abnormalities; T21, T18 (Edward’s) and T13 (Patau’s)
• costs $400-500
• 99% sensitivity and specificity

3 - Second trimester screening (not normally conducted anymore)

• combines maternal age, ß-HCG, uncojugated estradiol, and AFP +/- inhibin A (quadruple testing)
• involves a blood test which can be performed from 14-20 wks gestation
• test is reported as low or high risk
• has lower sensitivity (75%)

Question 5

Down syndrome counselling - Diagnostic options

Answer 5

Diagnostic options
1 - Chorionic villus sampling (CVS)
- test conducted during 1st trimester (usually 11-14 weeks)
- is a TA/TV US guided biopsy of chorionic villi on placenta for genetic testing
- mosaicism can give false neg/pos
- risk of miscarriage is 1/100
- other risks: infection rhesus, etc

2 - amniocentesis

• test is performed in second trimester (15-20 weeks)
• trans-abdominal US guided aspiration of amniotic fluid for fetal cells
• 1/200 risk of miscarriage