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.
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.
Down syndrome is famously detected through a first trimester screening test:
- Free beta-hCG
- Blood test
- 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.
The more definitive options are:
- Done earlier but presents greater risk to the foetus, because it’s about chopping off a bit of the chorionic villus
- 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
- 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].
- 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].
- BabyCenter Australia. (2018). Screening for Down syndrome. [online] Available at: https://www.babycenter.com.au/a1487/screening-for-down-syndrome [Accessed 31 Mar. 2018].