Three Major Trisomy Disorders

Trisomy 13: Patau syndrome

Trisomy 18: Edward syndrome

Trisomy 21: Down syndrome

Informative, right? Not yet! The real meat, or pseudo-meat if you’re not of a carnivorous sentiment, is in the memorising.

Memory Aids

Arrange these trisomies in order of increasing number: 13, 18, 21.

Then the mnemonic you need is: PED. As in pediatrics! As in children! Which is the patient demographic to whom these congenital trisomies relate.

The prevalence follows a similar trend; Patau syndrome is the most life-threatening but least common and those with Edward syndrome can live a tiny bit longer but not much so, while Down syndrome is more compatible with life and the most common of these three conditions.

Screening Tests

Down syndrome is famously detected through a first trimester screening test:

  • Free beta-hCG
    • Blood test
  • PAPP-A
    • Blood test
  • Nuchal translucency scan
    • Measures nuchal fold thickness, as this is greater in Down syndrome

NIPT is another option. It’s non-invasive prenatal testing that uses the mother’s blood.

Diagnostic Tests

The more definitive options are:

  • CVS
    • Done earlier but presents greater risk to the foetus, because it’s about chopping off a bit of the chorionic villus
  • Amniocentesis
    • Done later at half the risk of CVS, with the downside of the parents having to find out further into the pregnancy compared to CVS

References

  1. The University of Chicago Pediatrics Clerkship. (2018). Trisomy 18 (Edwards), Trisomy 13 (Patau). [online] Available at: https://pedclerk.bsd.uchicago.edu/page/trisomy-18-edwards-trisomy-13-patau [Accessed 31 Mar. 2018].
  2. Pregnancy, Birth and Baby. (2018). Screening for Down syndrome. [online] Available at: https://www.pregnancybirthbaby.org.au/screening-for-down-syndrome [Accessed 31 Mar. 2018].
  3. BabyCenter Australia. (2018). Screening for Down syndrome. [online] Available at: https://www.babycenter.com.au/a1487/screening-for-down-syndrome [Accessed 31 Mar. 2018].
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